By Matt Wood
Joseph Kirsner, MD, continues to report to work after 76 years as a gastroenterologist at the University of Chicago Medical Center. At 102, he must be doing something right. Sure, he keeps his mind and body active by keeping up with research and coming into the office. But how much of longevity is attributable to a healthy lifestyle and good genes, and how much is due to luck?
Two researchers at the Center on Aging at the University of Chicago have found that luck plays a significant role in living to 100. In a new study published in The Journal of Aging Research, they found that people born in September, October or November had higher odds to crack the century mark than those born in the spring.
Leonid Gavrilov, PhD, and his colleague and wife, Natalia Gavrilova, PhD, look for clues to longevity at the Center on Aging, which is part of NORC at the University of Chicago. They study potential predictors and determinants of human longevity, such as family background and environment. “It’s a way to get insights into mechanisms of aging and longevity, and hopefully to find new approaches to extend healthy human life,” Leonid Gavrilov said.
In past studies they found that chances for exceptional longevity are higher for U.S. citizens who were born to young mothers, had a slender or medium body build at age 30 and were farmers or spent their childhood on a farm. Studying pooled data about longevity for large populations can be tricky though.
“People from families with different ethnic, educational and income background may have somewhat different chances for long life,” Natalia Gavrilova said. “Also, different families may have slightly different seasonal patterns of births, because of religious and cultural traditions, holidays and vacation preferences.”
To control for unobserved differences between families in their latest study, they used a “within-family” approach by studying differences in life span between siblings within the same families, with the same parents and family background. They also studied spouses in the same families who lived together and shared their living conditions at adult age.
The study, supported by the National Institute on Aging, is based on data collected from Rootsweb, a publicly available repository of online genealogies. Using computer scripts to sift through the data, they found more than 2,800 families with enough information on birth and death dates of siblings to analyze. “The within-family approach significantly adds credibility to the claim that human longevity is indeed affected by the month of birth,” Leonid Gavrilov said.
How exactly it affects longevity isn’t clear yet, but Gavrilov said he has several hypotheses that he’d like to test. One possible explanation is maternal diet during pregnancy. Nutritional deficiencies during early development can have long-lasting effects later in life and play a major role in DNA damage, aging, and premature deaths from cancer and heart disease. Seasonal vitamin deficiencies in a mother’s diet during pregnancy, or the child’s diet during infancy, can affect longevity.
Another possible explanation is exposure to seasonal infections during pregnancy. Seasonal peaks for infections during spring and summer are common, and exposure to diseases such as German measles, chickenpox and poliovirus during gestation can result in birth defects.
Birth month can also influence longevity through climate, such as seasonal temperature and sun exposure. Experiencing higher summer temperatures during the first year of life can cause severe diarrhea and dehydration in infancy, with long-lasting effects. Higher temperatures at the time of conception can also affect sperm quality.
All of these factors mean that people born during the fall avoid the accumulation of birth defects, diseases and general wear and tear on the body that can limit life expectancy. Gavrilov said this highlights the importance of prenatal care and early life experiences. “The roots for overall health and adult survival are likely to be in human development during pregnancy and childhood,” he said. “This is the time when reserve capacity, numbers of functional cells and units, of different tissues and organs is determined, thus affecting physiological reliability and durability in later life.”
But while looking back at family histories helped find this link between birth month and longevity, the study found that the effect of the season of birth is declining for more recent generations. Modern diets are less seasonal than in the past, lessening the effects of seasonal nutritional deficiencies during pregnancy, and modern immunization regimens limit the impact of infectious diseases.
A group of researchers from Boston University recently studied the genomes of two 114-year-olds and found, surprisingly, that they were basically the same as other people’s. The secret to longevity may not lie exclusively in extraordinary genes, birth month or even luck. A whole host of genetic and environmental factors have to fall into place for someone to live past 60, let alone 100. “People with exceptional, healthy longevity represent the results of a successful, natural experiment on healthy life extension and delayed aging,” Gavrilov said. “We have to find out the secrets of longevity by studying deeply all the details of this natural experiment.”