Life After Full-time Work Blog

Which has a greater effect on your longevity, and from what age, in particular, do genetic factors start to dominate?

Every day we become a day older. That’s common sense, right? It’s simply counting. Two people born on the same day are the same age as each other, on any subsequent day. But, particularly as we age, it becomes apparent that some people appear noticeably older (or younger) than others of the same age. And perhaps a doctor will pronounce them to be much more (or less) healthy than others of the same age.

That’s the difference between your chronological and your biological age – a concept that my erudite friend Prof. Moshe Milevsky (a professor of finance at the Schulich School of Business at York University in Toronto) introduced me to. Essentially, your biological age is the average chronological age of people who have the same health characteristics as you do. So, for example, you may be 60 years old chronologically, but if your health is more like the health of an average 52-year-old, then your biological age is 52. Moshe has written a book called Longevity Insurance for a Biological Age: why your retirement plan shouldn’t be based on the number of times you circled the sun. Brilliantly expressed, because of course your chronological age is just the number of years you’ve completed, which in turn is the number of times you’ve circled the sun. And, as he says, your retirement plan should be based on the number of years you’re likely to live, which is of course really a function of your biological age much more than your chronological age.

But enough about that – it’s a diversion from my main topic, which is: which affects your lifespan (or, if you prefer, your biological age) more, your inherited genes or your lifestyle? Clearly they both are relevant. We know that people from long-lived families tend to outlive those from short-lived families, so genes must have an effect. And people with healthy lifestyles tend to outlive people with unhealthy lifestyles, so lifestyle too must have an effect. But my question is: which has the bigger effect? And how much bigger is that effect?

Yes, you can guess that I tried to research the subject.

I started by googling for the correlation between people’s ages at death and their parents’ ages at death. Here’s what I got, shown as “AI Overview”: “Research shows a strong positive correlation between a person’s age at death and the age at which their parents died, meaning that if a person’s parents lived to a relatively old age, they are more likely to live longer as well.” Oh, good. What’s that “strong positive” correlation? I couldn’t find a number. Immediately the references went to complicated explanations and studious papers with references to “the standard binary logit model” (whatever that is) and complicated stuff like that, rather than something like “the correlation in this study was +0.35” or whatever the number might have been (I made up that +0.35 number).

OK, then, let’s think about it a little bit. Many, if not most, deaths at younger ages are the results of accidents, and I wouldn’t think that genetics would play a noticeable role there. Google again. I was surprised to see this in the AI Overview: “Accidental death rates significantly increase with age, with the highest rates occurring among older adults, particularly those over 65, where falls are the primary cause of accidental deaths; younger individuals tend to have higher rates of accidental deaths from causes like motor vehicle accidents and unintentional poisoning, with the overall rate generally declining throughout adulthood until a sharp rise in later life.” My going-in thought was that accidental death rates would decline as age increased, but apparently not. And even with older adults (defined online as age 65+), there’s a dramatic increase in accidental death rates, the risk growing significantly with increasing age.

So, accidents are a big factor throughout. And I’d guess they wouldn’t be genetically influenced. So then, when would genetic factors start to come noticeably into play, meaning factors that help avoid, or at least postpone, age-related diseases?

Google again. AI Overview extract: “Studies estimate that genetics account for roughly 25% of variation in human longevity, meaning some individuals may inherit genes that contribute to a longer life compared to others.” (Nothing further on how that variation is measured, so no implication as to correlation. And no explicit reference to where that 25% number is cited. Too bad.)

OK, time for more detailed research.

I found a lot of stuff, and it took a long time. I won’t mention all the stuff that wasn’t helpful. Anyway, here’s what I found.

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In particular, there was a terrific article in the New York Times on January 8, 2025. Among other things, it provided a reference consistent with that 25% variability number. Fascinating: it came from a study of Danish twins, and the study said that “the heritability of longevity was estimated to be 0.26 for males and 0.23 for females.” The NYT article went further. It said that: “Overall, scientists think that how long we live is about 25 percent attributable to our genes, and 75 percent attributable to our environment and lifestyle. But as people near 100 and beyond, those percentages start to flip…” (But … I couldn’t find the age at which the genetic effect started to exceed the lifestyle effect.)

It also referred to another study (in the US) that measured the impact of elements of a healthy lifestyle on one’s longevity. Specifically, the study looked at the aggregate effect of five elements of a healthy lifestyle: never smoking; having a body mass index (BMI) in the range of 18.5 to 24.9; doing at least 30 minutes a day of moderate to vigorous physical activity; moderate alcohol intake (I had to check this out further! They meant 5 to 15 grams per day for women and 5 to 30 grams per day for men, 10 grams being a standard drink); and a high diet quality score (which it defined as being in the upper 40% – again, I tried to check this out, but got no further than a reference to National Health and Nutrition Examination Surveys). Oh, and the data came from more than 130,000 people, after they excluded those for whom complete data were unavailable: so, a very large survey, with random effects (I’m guessing) very small.

And what were those impacts? Very simply (and skipping past several pages of data analysis), those with those five healthy lifestyle elements were likely to prolong their future life expectancy at age 50 by 14.0 years for females and 12.2 years for males. Given that in 2014 (when the study was conducted) the future life expectancy for American 50-year-olds was 33.3 years for women and 29.8 years for men, this implied an increase to 47.3 years for healthy women (meaning: living to an average age of 97.3) and 42.0 years for healthy men (meaning: living to an average age of 92.0). Wow, that’s a lot! And it’s from lifestyle elements only.

Is there an age after which all of those who have survived thanks to a healthy lifestyle now start to benefit more from genetics? In other words, an age after which genetics play a larger part than a healthy lifestyle? I wish I could find such a reference, but I couldn’t. The best I got was: “Genetics play a significant role in influencing life expectancy after age 80, as research indicates that a person’s genetic makeup can account for roughly 20-30% of variation in lifespan, with this influence becoming more prominent in later years when lifestyle factors may have less impact on longevity; individuals with ‘good genes’ are more likely to live longer past 80 due to factors like efficient DNA repair, cell protection mechanisms, and reduced risk of age-related diseases.”

But that doesn’t answer my question. I’m guessing that age 80 showed up because age 80 is often considered the start of old age, and is a convenient dividing point in studies. And then onto an exploration of which specific genetic variations have an effect. When I searched for the numerical extent to which genetics influence longevity after age 80 the best I got was “significantly larger,” which doesn’t satisfy my numerical mind.

So there it is. If any of my readers can provide me with more insight, I’d appreciate it, because (as I’m sure you can tell) I’m eager to get numbers rather than undefined subjective words like “significantly larger.” And in particular, I’m seeking to discover the chronological age (quite possibly differing by sex and race and so on) at which genetics play a greater role than healthy living. For example: perhaps after age 80, meaning that up to age 80 lifestyle is more important factor than genetic inheritance, but once you’ve made it to age 80, your genetic inheritance starts to stand you in good stead and distinguish you (to some extent) from others who have followed your own healthy lifestyle.

But is it 80? Or some other age? That’s what I’m looking for.

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Takeaway

Lifestyle has a huge (indeed, dominant) effect until very late in life; but I couldn’t find an explicit reference to an age (80?) at which genetics start to have a larger effect.

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