Why females live longer than males

*Certain community characteristics may affect life expectancy
*Higher daily step counts lower mortality risk from all causes

An international team of scientists studying lifespans of wild mammals have found that, just like humans, females tend to live significantly longer than their male counterparts.

The researchers looked at the lifespans of 101 different species, from sheep to elephants, and found that females lived an average of 18 per cent longer than males for more than 60 per cent of the species studies. In humans, females tend to live around 7.8 per cent longer.

The study, led by scientists at University Lyon 1, France and published in the journal, Proceedings of the National Academy of Sciences, found this was not due to the sexes aging at different rates but that females had an average lower risk of mortality in adulthood than males.

It was unclear from the data as to why females survive longer than males, however the authors suggest that it could be due to complex interactions between the local environmental conditions and sex-specific costs of reproduction.

Prof. Tamás Székely, from the Milner Centre for Evolution at the University of Bath, was one of the authors of the study. He said: ‘We’ve known for a long time that women generally live longer than men, but were surprised to find that the differences in lifespan between the sexes were even more pronounced in wild mammals than in humans.

“This could be either because females are naturally able to live longer, or that female mortality drops compared with males.

“For example, lionesses live at least 50 per cent longer in the wild than male lions. We previously thought this was mostly due to sexual selection — because males fight with each other to overtake a pride and thus have access to females, however our data do not support this. Therefore there must be other, more complex factors at play.

“Female lions live together in a pride, where sisters, mothers and daughters hunt together and look after each other, whereas adult male lions often live alone or with their brother and therefore don’t have the same support network.

“Another possible explanation for the sex difference is that female survival increases when males provide some or all of the parental care. This is also true in birds. Giving birth and caring for young becomes a significant health cost for females and so this cost is reduced if both parents work together to bring up their offspring.”

The researchers plan to compare the data on wild animals with that of captive zoo animals, which do not have to deal with predators or competition for food or mates. This will allow them to measure the extent to which biological differences between the sexes have an effect on life expectancy.

“By affecting males and females differently, harsh environmental conditions such as a high prevalence in pathogens, is likely to cause sex-differences in lifespan.

“Comparing the sex gap in lifespan and aging across several populations of the same species is definitely full of promises,” said Jean-François Lemaître from the National Centre for Scientific Research (University Lyon 1, France) and coordinator of this study.

Meanwhile, in a new study, higher daily step counts were associated with lower mortality risk from all causes. The research team, which included investigators from the National Cancer Institute (NCI) and the National Institute on Ageing (NIA), both parts of the National Institutes of Health, as well as from the Centers for Disease Control and Prevention (CDC), also found that the number of steps a person takes each day, but not the intensity of stepping, had a strong association with mortality.

The findings were published March 24, 2020, in the Journal of the American Medical Association.

“While we knew physical activity is good for you, we didn’t know how many steps per day you need to take to lower your mortality risk or whether stepping at a higher intensity makes a difference,” said Pedro Saint-Maurice, Ph.D., of NCI’s Division of Cancer Epidemiology and Genetics, first author of the study. “We wanted to investigate this question to provide new insights that could help people better understand the health implications of the step counts they get from fitness trackers and phone apps.”

Previous studies have been done on step counts and mortality. However, they were conducted primarily with older adults or among people with debilitating chronic conditions. This study tracked a representative sample of U.S. adults aged 40 and over; approximately 4,800 participants wore accelerometers for up to seven days between 2003 and 2006. The participants were then followed for mortality through 2015 via the National Death Index. The researchers calculated associations between mortality and step number and intensity after adjustment for demographic and behavioral risk factors, body mass index, and health status at the start of the study.

They found that, compared with taking 4,000 steps per day, a number considered to be low for adults, taking 8,000 steps per day was associated with a 51 per cent lower risk for all-cause mortality (or death from all causes). Taking 12,000 steps per day was associated with a 65 per cent lower risk compared with taking 4,000 steps. In contrast, the authors saw no association between step intensity and risk of death after accounting for the total number of steps taken per day.

“At NIA, we’ve long studied how exercise is important for older adults, and it’s good to see further evidence from a large study with a broad sample that the main thing is to get moving for better overall health as we age,” said Eric Shiroma, Ph.D., a co-author and NIA Intramural Research Program scientist.

In analyses by subgroups of participants, the authors found that higher step counts were associated with lower all-cause death rates among both men and women; among both younger and older adults; and among white, black, and Mexican-American adults. In secondary outcomes of the study, higher step counts were also associated with lower rates of death from cardiovascular disease and cancer.

Data collection was conducted through the CDC’s National Health and Nutrition Examination Survey (NHANES), a program of studies designed to assess a nationally representative sample of the health and nutritional status of adults and children in the United States.

The researchers were surprised they didn’t find an association between higher stepping intensity and all-cause mortality after adjusting for the total number of steps per day. Because few studies have investigated an association between mortality and intensity among adults going about their daily lives, the study authors wrote that future studies of walking intensity and mortality are warranted.

Although the study authors controlled for factors that could have affected the results, the study is observational and cannot prove causality. Nevertheless, their findings are consistent with current recommendations that adults should move more and sit less throughout the day. Adults who do any amount of physical activity gain some health benefits. For even greater health benefits, adults are recommended to get at least 150 minutes of moderate-intensity physical activity per week.

“Being physically active has many benefits, including reducing a person’s risk of obesity, heart disease, type 2 diabetes, and some cancers. And on a daily basis, it can help people feel better and sleep better,” said Janet Fulton, Ph.D., of CDC’s Division of Nutrition, Physical Activity, and Obesity. “CDC is working with communities and partners across the country, as part of the Active People, Healthy Nation initiative, to make it easier, safer, and more convenient for people to be active in their own communities.”

Also, a new study suggests that certain community characteristics may affect life expectancy.

A team of researchers has found that community characteristics may have associations with people’s life expectancy.

The research, appearing in the journal Social Science & Medicine, suggests that authorities should consider taking these community characteristics, as well as other well-known predictors of life expectancy, into consideration when making policy.

According to the study, life expectancy in the United States had been increasing since the 1980s, as in many other parts of the world. However, in 2016, it began a two-year decline — the first time this had happened since 1962–63.

While, in absolute terms, United States (U.S.) experts predict life expectancy to grow during the next 40 years, they expect it to do so at a much slower rate than other countries.

If predictions are accurate, the U.S. will drop 21 spots in global life expectancy rankings from its current position of 43rd to 64th, meaning there will be a relative decline in life expectancy.

In addition to this, life expectancy varies significantly from region to region in the US, ranging from 56 to 97 years.

Understanding the factors for this relative decline in life expectancy, as well as the major variations across the country is crucial for policymakers.

Various individual health issues affect longevity, such as high levels of smoking, low levels of physical activity, and high levels of obesity. The research in the present study backed up these findings.

Many other factors affect life expectancy, such as income inequality.

These factors have complex relationships. For example, there are differences in mortality linked to gender; one study found that state-level factors might affect more women than men.

Dr. Elizabeth Dobis, a postdoctoral scholar at the Penn State College of Agricultural Sciences, Pennsylvania, is the lead author of the study.

She says, “American life expectancy recently declined for the first time in decades, and we wanted to explore the factors contributing to this decline. Because of regional variation in life expectancy, we knew community-level factors must matter.

“By analyzing place-based factors alongside personal factors, we were able to draw several conclusions about which community characteristics contribute most strongly to this variation in life expectancy.”

The present study focused on how the characteristics of a community, rather than individual traits, may affect life expectancy. It drew on data from 3,000 U.S. counties, looking at the variations in life expectancy from a 1980 baseline to 2014.

The researchers developed a statistical methodology to account for the various confounding factors that would also affect life expectancy. They tried to give as clear a picture as possible about the precise effect these community characteristics might have.

Although there was a clear relationship between life expectancy in 1980 compared with 2014, there were some unpredicted variations.

In Dobis’ words, “When we controlled for historical life expectancy, we found three additional community factors that each exert a significant adverse effect — a greater number of fast food restaurants, higher population density, and a greater share of jobs in mining, quarrying, and oil and gas extraction.

“For example, for every one percentage point increase in the number of fast food restaurants in a county, life expectancy declined by .004 years for men and .006 years for women.”

Conversely, the study found that greater access to health care, a population that is increasing in size, and high levels of social cohesion were all associated with higher life expectancies.

Stephan Groatz, professor of Agricultural and Regional Economics at Penn State, and a co-author of the study, comments on the findings. “Places with residents who stick together more on a community or social level also appear to do a better […] job of helping people, in general, live longer.”

However, there are limits to the study’s findings. While the study makes clear associations between community characteristics and life expectancy, it is not necessarily clear why or how these affect longevity, nor is it clear how they might interact with other factors.

And from a policy perspective, understanding specific community characteristics may be helpful. Still, policymakers need to understand larger trends and factors if they want to prevent the continued decline of life expectancy.

Nonetheless, the study lays the groundwork for future research, highlighting some factors that researchers might want to analyse in more detail.