1 in 10 global cardiovascular deaths due to high sodium intake

The World Health Organization recommend that adults should consume less than 2 g of sodium per day. But a new study finds that sodium intake above this recommendation accounts for almost 1 in 10 cardiovascular deaths globally each year.

Researchers estimate that 1 in 10 cardiovascular deaths each year are attributable to sodium intake above the WHO recommendations of 2 g per day.

The research team, led by Dr. Dariush Mozaffarian of the Friedman School of Nutrition Science and Policy at Tufts University in Medford, MA, recently published their findings in The New England Journal of Medicine.

Sodium is an element that occurs naturally in most foods, such as table salt, milk, beets and celery. It is also added in high amounts to processed foods, including bread and processed meats.

Too much dietary sodium can increase blood pressure, and high blood pressure is a major risk factor for cardiovascular diseases, such as heart disease and stroke.

"However," says Dr. Mozaffarian, "the effects of excess sodium intake on cardiovascular diseases globally by age, sex, and nation had not been well established."

Excess sodium intake attributable to 1.65 million cardiovascular deaths worldwide

To gain a better insight into how excess dietary sodium influences cardiovascular health on a global scale, the research team analyzed data from 205 surveys of sodium intake representing approximately 75% of the world's adult population.

They also assessed global nutrition data in order to see how sodium intake varies by sex, age and country. Furthermore, they conducted pooled meta-analyses to measure the effects of sodium on blood pressure, and separately, the effects of blood pressure on cardiovascular diseases.

The team's findings were applied to current global rates of cardiovascular diseases, and they used this information to estimate how many deaths are caused by sodium intake above 2 g per day.

Results of the study revealed that the average worldwide sodium intake in 2010 was 3.95 g per day - almost double the daily recommendation set by the World Health Organization (WHO).

All worldwide regions had sodium intakes above the WHO recommendation. These ranged from 2.18 g per day in sub-Saharan Africa to 5.51 g per day in Central Asia.

This excess sodium intake was attributable to 1.65 million cardiovascular-related deaths worldwide - the equivalent to 1 in 10 deaths from cardiovascular causes.

The researchers found that 4 out of 5 global deaths attributable to excess sodium intake occurred in low- and middle-income countries.

How is the US affected by sodium intake?

The average daily sodium intake in the US was almost 80% higher than the WHO recommendation, at 3.6 g, and significantly higher than the 2.3 g per day intake recommended by the federal government's Dietary Guidelines for Americans.

In addition, the researchers found that daily sodium intake above 2 g accounts for around 58,000 cardiovascular-related deaths in the US each year.

Commenting on the results, study author John Powles, of the department of public health and primary care at the University of Cambridge in the UK, says:

"These new findings inform the need for strong policies to reduce dietary sodium in the United States and across the world."

From their meta-analyses, the researchers found that reducing sodium intake lowered blood pressure in all adults, particularly among blacks, older adults and those who already had high blood pressure.

"Programs to reduce sodium intake could provide a practical and cost-effective means for reducing premature deaths in adults around the world," adds Powles.

The team notes that their study is subject to some limitations. For example, estimates of sodium intake were based on urine samples, which could have underestimated actual sodium consumption.

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Memories of error 'improve our learning speed'

Researchers at Johns Hopkins Medicine in Baltimore, MD, think they have discovered why people learn an identical task faster on subsequent attempts. Publishing their findings in Science Express, the team says our memories of error are the key to faster learning.

The scientific name for the small differences between our expectations of an action and the reality of that action is "prediction errors."

The researchers note that when people perform a task - such as opening a door - their brains make comparisons of how the door moved with how they expected the door to move. This information is calculated in a way that allows the person to perform the task more efficiently next time.

The scientific name for the small differences between our expectations of an action and the reality of that action is "prediction errors." We learn prediction errors in a largely unconscious way.

To further investigate how the brain learns prediction errors, the researchers devised an experiment involving a joystick and a pair of dots on a screen.

The participants were told to guide a blue dot toward a red dot on the screen using the joystick. However, the participants were unable to see the joystick that they were holding, and the blue dot could also be programmed by the researchers to move in an off-kilter way.

To overcome the off-kilter movement of the dot, the participants were required to compensate their joystick movements accordingly. Typically, after a few attempts, they would adjust their movements to guide the blue dot to its target.

The researchers observed that the participants responded more quickly to small errors that pushed them consistently in one direction than to larger errors that were less consistent.

David Herzfeld, a graduate student in Shadmehr's laboratory who led the study, explains: "They learned to give the frequent errors more weight as learning cues, while discounting those that seemed like flukes."

Reza Shadmehr, PhD, a professor in the Department of Biomedical Engineering at Johns Hopkins, compares the experiment to his proficiency as a tennis player.

"I'm much better in my second 5 minutes of playing tennis than in my first 5 minutes," he says, "and I always assumed that was because my muscles had warmed up. But now I wonder if warming up is really a chance for our brains to re-experience error."

'Two processes happening simultaneously'

Further explaining the experience of learning a new motor task, Dr. Shadmehr says there appear to be two processes happening simultaneously. One of these is the learning of motor commands, and the other is critiquing the learning, "much the way a 'coach' behaves."

"Learning the next similar task goes faster, because the coach knows which errors are most worthy of attention. In effect, this second process leaves a memory of the errors that were experienced during the training, so the re-experience of those errors makes the learning go faster."

Daofen Chen, PhD, a program director at the National Institute of Neurological Disorders and Stroke, who co-funded the study, says that the research is a significant step toward understanding how we learn motor skills:

"The results may improve movement rehabilitation strategies for the many who have suffered strokes and other neuromotor injuries."

In the next component of the research, the team will examine which brain region is responsible for the "coaching" role in assigning different weights to various types of error.

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Exercise for the heart may also protect the mind

 It would appear that aerobic exercise may do more than just preserve our cardiovascular health - it may also keep our minds sharp as we age. This was the conclusion of a new study from Canada that found links between aerobic fitness and brain function in older adults.

The researchers, including first author Dr. Claudine Gauthier and others from the University of Montreal, report their findings in the journal Neurobiology of Aging.

Dr. Gauthier, now a post-doctoral fellow at the Max Planck Institute for Human Cognitive and Brain Sciences in Germany, explains:

"Our body's arteries stiffen with age, and the vessel hardening is believed to begin in the aorta, the main vessel coming out of the heart, before reaching the brain. Indeed, the hardening may contribute to cognitive changes that occur during a similar time frame."

Older adults with more elastic aortas performed better on mental tests

She and her fellow researchers studied a group of older adults and found the ones whose aortas were in better condition and who were aerobically fitter did better on a cognitive test:

A group of older adults who were aerobically fitter performed better on a cognitive test, researchers say.

"We therefore think that the preservation of vessel elasticity may be one of the mechanisms that enables exercise to slow cognitive aging," she adds.

They studied two groups of physically and mentally healthy participants: 31 younger people aged 18-30 and 54 older adults aged 55-75.

They were interested in comparing not only the younger to the older group, but also to make comparisons within each age group.

All participants underwent physical and mental tests. For the physical tests, they worked hard on workout machines while the researchers measured their maximum oxygen intake over 30-second periods. And for the mental test, they performed a Stroop effect task - a scientifically validated test researchers often use to measure cognitive ability.

In the Stroop effect test, the participant is shown the names of different colors, such as RED, YELLOW, BLUE, and so on, with each word printed in a color that is not the color meant by the word. Thus, RED might be printed in blue, and YELLOW might be printed in red. The participant has to shout out the color of the print and not the printed word.

The participants also underwent three MRI scans: one measured blood flow to the brain, another measured brain activity during the Stroop task, and the third measured the stiffness of the aorta. The aorta is the largest blood vessel in the body - it carries oxygen-rich blood away from the heart to the rest of the body.

The researchers found evidence of age-related declines in brain executive function, elasticity of the aorta and cardiorespiratory fitness. They also found links between vascular health and brain function, and aerobic fitness and brain function.

Method could be adapted to study links in less healthy populations

Dr. Gauthier says this is the first study to report using MRI in this way:

"It enabled us to find even subtle effects in this healthy population, which suggests that other researchers could adapt our test to study vascular-cognitive associations within less healthy and clinical populations."

She notes that although other, more complex mechanisms may also link cardiovascular fitness and the health of blood vessels in the brain, "overall these results support the hypothesis that lifestyle helps maintain the elasticity of arteries, thereby preventing downstream cerebrovascular damage and resulting in preserved cognitive abilities in later life."

Funding for the study came from a number of sources, including the Canadian Institutes for Health Research, the Canadian Foundation for Innovation, the Canadian National Sciences and Engineering Research Council, and the Ministère du développement économique, de l'innovation et de l'exportation.

Meanwhile, in another recently published study led by Stanford University, Medical News Today learned how physical activity cuts the risk of irregular heartbeat in older women. The researchers found the more physically active the women were, the lower the chance they would develop atrial fibrillation, a heart condition that causes arrhythmia.

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Will losing weight really make you happier?

Although physical health is significantly improved by weight loss, the effects of losing weight on mental health are less clear, according to a new study by University College London researchers in the UK.

"People should not expect weight loss to instantly improve all aspects of life," say the researchers.

The study, which is published in the journal PLOS ONE, looked at 1,979 overweight and obese people in the UK.

It found that people who lost 5% or more of their original weight over 4 years showed significantly improved physical health. However, these people were more likely to report low mood than participants who stayed within their initial weight.

In the study, 14% of the participants lost at least 5% of their body weight - the mean weight loss was 6.8 kg per person.

Adjusting their results to take into account serious health issues and major life events that might cause weight loss and depressed mood, the researchers calculated that the participants who lost weight were 52% more likely to report symptoms of depression.

Lead author Dr. Sarah Jackson, of University College London's Epidemiology and Public Health department, says:

"We do not want to discourage anyone from trying to lose weight, which has tremendous physical benefits, but people should not expect weight loss to instantly improve all aspects of life."

She adds that "aspirational advertising by diet brands" may set unrealistic expectations about weight loss by offering what appear to be instant life improvements. Dr. Jackson advises that people should be realistic about weight loss and be prepared for the challenges:

"Resisting the ever-present temptations of unhealthy food in modern society takes a mental toll, as it requires considerable willpower and may involve missing out on some enjoyable activities. Anyone who has ever been on a diet would understand how this could affect well-being.

However, mood may improve once target weight is reached, and the focus is on weight maintenance. Our data only covered a 4-year period so it would be interesting to see how mood changes once people settle into their lower weight."

She also says that health care professionals should monitor both the physical and mental health of patients when recommending weight loss and offer ongoing support as needed.

What were the study's limitations?

Although the researchers attempted to factor in major life events that could confound results, such as bereavement, which is known to be associated with both weight loss and depression, they acknowledge that data on this was limited.

The bereavement data only covered parents and spouses during the study, and did not take into account deaths of children, close friends or non-marital partners, or the deaths of parents or spouses shortly before the study commenced.

Another major life event that the study did not have data for that could have caused weight loss and depression was job loss.

The study participants were predominantly white, older adults. It is possible, therefore, that the effects of weight loss might be different among different ethnic groups or younger adults.

Also, the researchers admit problems with the measure of well-being used in the study, explaining:

"The use of an arbitrary, unvalidated threshold to indicate low levels of well-being is also problematic, and we observed some differences in results when well-being data were analyzed continuously, so these results should be interpreted with caution."

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Baldness cured with bone marrow disease drug in alopecia areata patients

Alopecia areata causes hair loss for more than 6.5 million people in the US. Now, researchers have discovered that a drug already approved by the Food and Drug Administration for treatment of a rare bone marrow disease - ruxolitinib - could restore hair growth in these patients.

Researchers found that a drug used to treat a rare bone marrow disease - ruxolitinib - restored the hair of patients with alopecia areata within a few months.
Image credit: Columbia University Medical Center

The research team, led by Dr. Raphael Clynes and Angela M. Christiano of Columbia University Medical Center (CUMC), recently published the initial findings of their ongoing clinical trial in the journalNature Medicine.

"We've only begun testing the drug in patients, but if the drug continues to be successful and safe, it will have a dramatic positive impact on the lives of people with this disease," says Dr. Clynes.

Alopecia areata is a disease whereby the immune system attacks hair follicles - the parts of the skin from which hair grows. The majority of people with this disease experience bald patches over their head, face and body, although the condition can cause total hair loss in some cases.

It is unclear exactly what causes the disease, but this latest study may shed some light, as well as offer a potential treatment.

FDA-approved drugs 'fully restored hair in mice within 12 weeks'

Four years ago, the CUMC team conducted a study of more than 1,000 patients with alopecia areata. Their findings indicated that hair follicles send a "danger signal" to immune cells, which encourages them to launch an attack on the follicles.

The researchers investigated this further by studying mice with the disease. By tracing the danger signal backwards, they identified a certain set of T cells responsible for attacking hair follicles.

Through further research into cells of both mice and patients with the disease, the team pinpointed several immune pathways through which these T cells launch their attack. These pathways, the researchers say, can be targeted by a class of drugs known as JAK inhibitors.

The researchers tested two JAK inhibitors already approved by the Food and Drug Administration (FDA) - ruxolitinib (approved for the treatment of myelofibrosis, a rare bone marrow disease) and tofacitinib (approved for the treatment of rheumatoid arthritis) - on mice with alopecia areata that had severe hair loss from the disease.

These drugs, the researchers say, fully restored the rodents' hair within 12 weeks. Furthermore, this hair regrowth lasted for months after treatment had ceased.

Ruxolitinib restored patients' hair within 4-5 months

In this latest study, the researchers report on the findings of a small, open-label clinical trial of ruxolitinib on patients with moderate-to-severe alopecia areata, defined as having more than 30% hair loss.

Early results of the trial revealed that in three of the participants, hair growth was fully restored within 4-5 months of treatment initiation. Furthermore, the T cells that attack the hair follicles were no longer present in the participants' scalps.

Dr. Clynes says that although further testing is needed to determine whether ruxolitinib can be used for patients with alopecia areata, the findings so far are "exciting news" for those with the disease.

Commenting on the team's findings, Dr. David Bickers, of the Department of Dermatology at CUMC, says:

"There are few tools in the arsenal for the treatment of alopecia areata that have any demonstrated efficacy. This is a major step forward in improving the standard of care for patients suffering from this devastating disease."

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Women who read Fifty Shades 'more likely to have unhealthy behaviors'

Mr Grey will see you now." Just these words are likely to send many women into a frenzy. The Fifty Shades novels by British author E.L. James have been a global phenomenon, selling more than 100 million copies worldwide. But although reading a book may seem harmless, a new study suggests young adult women who read these erotic novels are more likely to engage in unhealthy behaviors that are risk factors for abusive relationships.

Women who read Fifty Shades are more likely to have unhealthy behaviors that are risk factors for abusive relationships, according to new research.

For those of you who are unfamiliar with Fifty Shades, the story revolves around the sexual endeavors of two characters: Anastasia Steele and Christian Grey.

In the first of the series - Fifty Shades of Grey - Steele, a literature student described as "unworldly" and "innocent," meets Grey, a man who is charming, intelligent, but who has a dark, controlling side.

They then embark in a "daring, passionately physical" affair, or as lead study author Amy Bonomi of Michigan State University deems it, an abusive relationship. This continues throughout the subsequent two novels - Fifty Shades Darker andFifty Shades Freed.

According to the researchers, the erotic series "depicts pervasive violence against women, perpetuating a broader social narrative that normalizes these types of risks and behaviors in women's lives."

Is there a relationship between reading these books and unhealthy behaviors in real life? Bonomi and colleagues from The Ohio State University wanted to find out.

Fifty Shades fans 'more likely to binge drink, have abusive partners and eating disorders'

For their study, recently published in the Journal of Women's Health, the team analyzed 655 women between the ages of 18 and 24 - a time in women's lives when they are most likely to explore greater sexual intimacy in relationships, according to Bonomi.

Of these women, 122 had read all three Fifty Shades novels, 97 had read at least the first novel but not all three, and 436 had not read any part of the novels.

The team found that, compared with women who had not read any of the books, the women who had read the first novel were 25% more likely to have a partner who verbally abused them, 34% more likely to have a partner who showed stalking tendencies, and 75% more likely to have starved themselves for more than 24 hours or to have used dieting aids.

Furthermore, women who had read all three books were 65% more likely to engage in binge drinking - defined as drinking five or more drinks in one sitting on 6 days or more every month - and were 63% more likely to have had five or more sexual partners in their lifetime, compared with those who had not read any of the books.

Bonomi admits that one limitation of this study is that they were not able to determine whether these behaviors were already pre-existing among the women. But she says that even if they were, reading the books may still pose problems.

She explains:

"If women experienced adverse health behaviors such as disordered eating first, reading Fifty Shades might reaffirm those experiences and potentially aggravate related trauma.

Likewise, if they read Fifty Shades before experiencing the health behaviors seen in our study, it's possible the books influenced the onset of these behaviors."

Unhealthy behaviors 'risk factors for abusive relationships'

Bonomi notes that she is not recommending that the book should be banned, nor is she trying to dictate what books women should or should not read.

But she says it is important that women understand that the unhealthy behaviors linked to reading Fifty Shades demonstrated in this study are risk factors for engaging in violent relationships.

In an attempt to reduce these risks, Bonomi says that parents and teachers should have conversations with children from a young age about sexuality and expectations of body image and gender roles.

In addition, she believes children and young adults should be taught to be critical when it comes to watching movies, reading books or consuming other media that demonstrates violence.

"We recognize that the depiction of violence against women in and of itself is not problematic, especially if the depiction attempts to shed serious light on the problem," Bonomi adds. "The problem comes when the depiction reinforces the acceptance of the status quo, rather than challenging it."

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Laughter may be the best medicine for age-related memory loss

We are all familiar with the saying, "laughter is the best medicine." And this motto may ring true when it comes to tackling age-related memory loss; a new study from Loma Linda University in California finds that humor may reduce brain damage caused by the "stress hormone" cortisol, which in turn, improves memory.

The research team, led by Dr. Gurinder Singh Bains, recently presented their findings at the Experimental Biology meeting in San Diego.

It is well known that too much stress can negatively affect health. Medical News Today recently reported on a study suggesting that stress may worsen allergies, while other research indicates that it makes the brain more susceptible to mental illness.

Past research has also shown that stress can worsen memory and learning ability in elderly individuals. This is because stress increases production of cortisol - a hormone that can cause damage to neurons in the brain.

Since it is well known that laughter can be a stress reliever, the research team wanted to determine whether humor may reduce brain damage caused by cortisol.

Watching a funny video 'reduced cortisol levels and boosted memory performance'

The researchers analyzed one group of elderly individuals who had diabetes and another group of elderly people who were healthy.

Laughter may reduce neuron damage caused by "stress hormone" cortisol, therefore improving memory in older individuals.

Both groups were required to view a 20-minute humorous video, before completing a memory test that measured their visual recognition, learning ability and memory recall.

A third group of elderly individuals were asked to complete the memory test without watching the funny video. The team then compared the results of all three groups.

Cortisol levels for all participants were recorded before and after the experiments.

The investigators found that both groups who watched the humorous video showed a significant reduction in cortisol levels, compared with the group that did not view the video.

The groups that watched the funny video also showed greater improvement in memory recall, learning ability and sight recognition, compared with those who did not watch the video. The diabetic group demonstrated the greatest improvement in both cortisol levels and memory test scores.

'Laughter may improve memory and quality of life'

Study co-author Dr. Lee Burk says these findings suggests that the less stress a person has, the better their memory performance, and humor may be the key to reducing stress levels.

"Humor reduces detrimental stress hormones like cortisol that decrease memory hippocampal neurons, lowers your blood pressure, and increases blood flow and your mood state," he explains.

"The act of laughter - or simply enjoying some humor - increases the release of endorphins and dopamine in the brain, which provides a sense of pleasure and reward."

He says that these neurochemical changes in the brain also increase "gamma wave band frequency," which can improve memory.

"So, indeed," he adds, "laughter is turning out to be not only a good medicine, but also a memory enhancer adding to our quality of life."

Dr. Bains says the team's findings may offer benefits that can be applied to wellness programs for elderly individuals, adding:

"The cognitive components - learning ability and delayed recall - become more challenging as we age and are essential to older adults for an improved quality of life: mind, body and spirit.

Although older adults have age-related memory deficits, complimentary, enjoyable and beneficial humor therapies need to be implemented for these individuals."

Laughter may not be the only way to boost memory. Medical News Today recently reported on a study suggesting that green tea may improve working memory, while other research from Johns Hopkins University in Maryland found that caffeine may boost long-term memory.

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Dose of measles virus destroys woman's incurable cancer

In what they describe as a proof of principle study, doctors in the US were able to keep a woman with deadly multiple myeloma - an incurable bone marrow cancer - free of all signs of living cancer cells for over 6 months by giving her just one high dose of measles virus.

Two patients received a single intravenous dose of measlesvirus that was engineered to kill myeloma plasma cells and not harm other cells.

The team, from the Mayo Clinic in Rochester, MN, says both patients responded to the treatment, showing reduced bone marrow cancer and levels of myeloma protein.

But one patient, a 49-year-old woman, experienced complete remission and remained disease-free for over 6 months.

A report on this first study to establish the feasibility of the treatment appears in the journal Mayo Clinic Proceedings.

Proof virotherapy works for disseminated cancer

First author Dr. Stephen Russell, hematologist and co-developer of the therapy, says:

"This is the first study to establish the feasibility of systemic oncolytic virotherapy for disseminated cancer. These patients were not responsive to other therapies and had experienced several recurrences of their disease."

The treatment is an example of oncolytic virotherapy - using engineered viruses to fight cancer - an approach that dates back to the 1950s. Thousands of patients have received this type of therapy, using oncolytic viruses from various families, including common cold viruses, herpes viruses and pox viruses.

But the authors say this is the first well-documented case of a patient with cancer that has spread experiencing complete remission at all disease sites after receiving oncolytic virus therapy.

Myeloma is a cancer that develops in plasma cells - a type of blood cell made in the bone marrow. According to the American Cancer Society, the disease is relatively uncommon, and in the US, there is a 1 in 149 risk of developing it.

Myeloma can arise in any part of the body where there is bone marrow, including the spine, rib cage and pelvis. Multiple myeloma means it is occurring in more than one place.

The disease, which also causes skeletal or soft tissue tumors, usually responds to drugs that stimulate the immune system, but it eventually overcomes them and is rarely cured.

First use of highest possible dose of engineered measles virus

Dr. Russell and colleagues explain in their article that they chose to report these two cases in particular because they were the first patients they had studied who had received the highest possible dose, and with limited previous exposure to measles, so their immune systems did not have many antibodies to the virus. They had also exhausted other treatment options.

Senior author Dr. Angela Dispenzieri, an expert in multiple myeloma, says in very simple terms, the measles virus makes the cancer cells join together and explode. The treatment also appears to trigger another lasting benefit:

"There's some suggestion that it may be stimulating the patient's immune system to further recognize the cancer cells or the myeloma cells and help mop that up more effectively than otherwise."

Having effectively completed a phase I clinical trial - to prove the concept that the measles virus can fight cancer - the team is now moving quickly into a phase II trial involving more patients.

They also intend to test the virus's effectiveness as a tool to fight other cancers, such as head and neck, brain and ovarian cancers and mesothelioma. And they are engineering other viruses that may be able to kill cancer cells.

Dr. Russell says they have recently started to think along the lines of "a single shot cure for cancer, and that's our goal with this therapy."

He and two other authors of the study, as well as the Mayo Clinic, have declared a financial interest in the methods used in the study, which was funded by the National Cancer Institute of the National Institutes of Health, Al and Mary Agnes McQuinn, The Harold W. Siebens Foundation and The Richard M. Schulze Family Foundation.

Medical News Today recently reported on a study in Nature Genetics, where scientists from The Institute of Cancer Research in the UK found a gene involved in aging is linked to multiple myeloma. The team said the discovery brings the total genetic variants linked to myeloma to seven and may help establish the genetic causes of the disease.

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Why was 1918 flu pandemic so deadly? Research offers new clue

In 1918, as one global devastation in the shape of World War I came to an end, people around the world found themselves facing another deadly enemy, pandemic flu. The virus killed more than 50 million people, three times the number that fell in the Great War, and did this so much faster than any other illness in recorded history.

But why was that particular pandemic so deadly? Where did the virus come from and why was it so severe? These questions have dogged scientists ever since. Now, a new study led by the University of Arizona (UA) may have solved the mystery.

Michael Worobey, a professor in UA College of Science's Department of Ecology and Evolutionary Biology, and colleagues describe their findings in the Proceedings of the National Academy of Sciences.

They hope the study not only offers some new clues about the deadliness of the 1918 pandemic, but will also help improve strategies for vaccination and pandemic prevention, as Prof. Worobey explains:

"If our model is correct, then current medical interventions, especially antibiotics and vaccines, against several pneumonia-causing bacteria, could be expected to dramatically reduce mortality, if we were faced today with a similar set of pandemic ingredients."

The 1918 pandemic killed predominantly young adults

One of the questions that has been particularly vexing is why the 1918 pandemic human influenza A virus killed so many young adults in the prime of life, he says, adding: "It has been a huge question whether there was something special about that situation, and whether we should expect the same thing to happen tomorrow."

Researchers reconstructed the origins of the 1918 pandemic virus, the classic swine flu and the postpandemic seasonalH1N1 flu virus lineage that circulated between 1918 and 1957, to find out why the 1918 pandemic was so deadly.

Usually, the human influenza A virus is deadlier to infants and the elderly. But the 1918 strain killed many people in their 20s and 30s, who mainly died from secondary bacterial infections, especially pneumonia.

For their investigation, the researchers developed an unprecedentedly accurate "molecular clock," a technique that looks at the rate at which mutations build up in given stretches of DNA over time.

Evolutionary biologists use molecular clocks to reconstruct family trees, follow lineage splitting and find common ancestors of different strains of viruses and other organisms.

Prof. Worobey and his team used their molecular clock to reconstruct the origins of the 1918 pandemic virus, the classic swine flu and the postpandemic seasonal H1N1 flu virus lineage that circulated between 1918 and 1957.

Genetic material from bird flu virus picked up just before 1918

They found that a human H1 virus that had been circulating among humans since around 1900 picked up genetic material from a bird flu virus just before 1918 and this became the deadly pandemic strain.

Exposure to previous strains of flu virus does offer some protection to new strains. This is because the immune system reacts to proteins on the surface of the virus and makes antibodies that are summoned the next time a similar virus tries to infect the body.

But the further away the new strain is genetically from the ones the body has previously been exposed to, the more different the surface proteins, the less effective the antibodies and the more likely that infection will take hold.

This is what the authors suggest happened to the young adults in the 1918 pandemic. In their childhood around 1880 to 1900, they were exposed to a supposed H3N8 virus that was circulating in the population. This virus had surface proteins that were very different from those of the H1N1 pandemic strain. Their immune system would have made antibodies, but they would have been ineffective against the H1N1 virus.

But people born either before or after those decades would have been exposed to a virus much more like the 1918 one and their immune systems were thus better equipped to fight it.

Prof. Worobey notes:

"We believe that the mismatch between antibodies trained to H3 virus protein and the H1 protein of the 1918 virus may have resulted in the heightened mortality in the age group that happened to be in their late 20s during the pandemic."

He says their finding may also help explain differences in patterns of mortality between seasonal flu and the deadly H5N1 and H7N9 bird flu viruses.

The authors suggest perhaps immunization strategies that mimic the often impressive protection that early childhood exposure provides could dramatically reduce deaths from seasonal and new flu strains.

In February 2014, Prof. Worobey and colleagues began challenging conventional wisdom about flu outbreaks, when in the journal Nature, they reported the most comprehensive analysis to date of the evolutionary relationships of flu virus across different host species over time.

Among other things, they challenged the view that wild birds are the major reservoir for the bird flu virus. Instead of spilling over from wild birds to domestic birds, they say the more likely scenario is the other way around - that new strains jump from domestic to wild birds.

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