Not long ago, a handful of scientists at the University of California at Irvine were curious about why some people live longer than others -- even within groups that have similar ethnic and educational backgrounds, disease risk profiles and are exposed to similar stressors in life. At heart, they knew the question is impossible to answer. People are complex. The effects of life events on our genes and lifespan -- what we eat, what we breathe, who we love, how we're loved and so on -- are impossible to isolate completely.
But the researchers had a hunch that some of us had a bad start -- beginning in the womb -- because our mothers were highly stressed during pregnancy. There's an avalanche of evidence that women who are under extreme duress in pregnancy have kids who have shorter attention spans, lower IQs, memory deficiencies and health problems.
Could prenatal stress also set a baby's life expectancy clock to tick faster?
One way to find out is to look at the genes of people whose mothers were extremely stressed during pregnancy. In each of our cells are DNA-protein complexes called telomeres that are attached to the end of chromosomes. Telomeres are often compared to the plastic aglet, or cap, at the end of a shoelace to keep it from fraying. Each time a cell divides, the telomere cap shortens. This makes telomeres something of a longevity marker. People with long caps at the end of their DNA strands tend to live longer than people who have short caps. Young people generally have longer caps than old people, and healthy people have longer caps than those less healthy. It doesn't matter how long your shoelace is; what counts is the length and integrity of the cap.
In the UCI study, researchers recruited nearly one hundred volunteers in their twenties. About half were selected because their mothers experienced a horrid event during pregnancy. The scientists weren't looking for the normal pregnancy stressors -- work-life balance, weight gain, fretting about the baby's health and so on. They meant extreme stressors: a sudden divorce, a death in the family, a natural disaster, and physical or emotional abuse.
What they found is disturbing.
Compared to the control group (whose moms had a relatively stress-free pregnancy), people who were once exposed to extreme prenatal stress had significantly shorter telomeres.
The difference was drastic. By our mid-twenties, most of us lose about 60 base pairs of telomere length annually. Not so of people who were exposed to extreme prenatal stress -- they lose catastrophically more telomeres each year. The men had 178 fewer base pairs on average (equivalent to 3.5 additional years of aging). Strikingly, it appears that a mother's prenatal stress hits her daughter harder than her son. The women had a shocking 295 base-pair deficit (5 years of accelerated aging).
How does this happen? During pregnancy, stress may alter blood flow, oxygen, and glucose metabolism between mother and baby. High levels of the stress hormone cortisol from the mother flood the placental barrier. Both these conditions affect the fetus's developing body and brain. Excess cortisol may also slow down the production of telomerase, an enzyme that acts as a repair kit for telomeres. Telomerase adds telomeric DNA to shortened telomeres. Essentially, it rebuilds caps. By extension, it regenerates our cells and tissues. Like a fountain of youth, telomerase gives back what time takes away.
So what if you're on a telomerase-less trajectory?
Here's the big relief: Your clock doesn't have to keep ticking so quickly, even if it has been set that way prenatally. There's strong evidence that lifestyle changes can amp up telomerase production. One study found that stress management, counseling and a healthy diet are associated with higher telomerase activity. Another -- to the delight of Buddhists -- found that meditation turns up the telomerase dial .
In the research community there's much interest in the idea that a gene therapy involving telomerase might someday reverse or prevent aging. This would offset ill effects of prenatal stress on lifespan. Or maybe more of us will embrace meditation -- and simply transcend time.
If you like this blog, click here for previous posts. If you wish, check out my new book, Do Chocolate Lovers Have Sweeter Babies?: The Surprising Science of Pregnancy.