If you woke up one morning in your mid-forties and found that two pints now did the work of four, and that your knees had started sending complaints, you may not have been imagining it. A Stanford Medicine study suggests the body doesn’t age at a steady pace. It seems to change in bursts, and the first big one arrives at around 44.
The second comes at around 60. If you’re reading Midcent, you’ve either been through one of them, you’re in the middle of one, or one is on its way. So here’s what the research found, how much weight it can carry and what you can sensibly do about it.
What did the Stanford study on ageing at 44 and 60 actually find?
The study, led by the geneticist Michael Snyder and published in Nature Aging in August 2024, followed 108 adults in California aged between 25 and 75. Over several years they gave repeated samples: blood, stool, skin swabs and others. The researchers tracked more than 135,000 different molecules and microbes, from proteins and fats to the bacteria in your gut.
The textbook assumption is that ageing happens in a straight line, with a little more wear every year. That isn’t what they saw. Most of the molecules they tracked, roughly four in five, changed in a non-linear way. There were quieter stretches, and then two periods of much bigger change, averaging around the mid-forties and the early sixties.
The team first suspected the mid-forties shift was down to the menopause. But the men in the study showed it too, so hormones in women can’t be the whole explanation. Something else is going on, and it affects you as well.
What changes in your mid-forties?
Around 44, the biggest changes were in molecules linked to how the body handles fats (lipids), alcohol and caffeine. There were also shifts in markers linked to cardiovascular disease, and in those linked to skin and muscle.
If you’ve noticed hangovers getting crueller, the afternoon coffee keeping you up at night or your cholesterol result creeping upwards, this fits. It doesn’t prove the study explains your hangover. But it’s a plausible biological backdrop to things a lot of men in their forties notice.
Don’t read too much into the exact number, though. The researchers aren’t saying everything changes on your 44th birthday. These are averages across a group, and individuals will vary.
And what happens at 60?
The second wave, in the early sixties, involved molecules tied to carbohydrate metabolism (how you process sugars and starches), the immune system and kidney function. Heart, skin and muscle markers shifted again too.
That lines up neatly with what doctors already see. The risk of type 2 diabetes rises with age, immune responses weaken, kidney function slowly declines and muscle loss speeds up unless you do something about it. The study doesn’t tell us anything clinically new here. What it does is suggest the decline may be lumpy rather than smooth.
Your body may age in bursts, but the dull habits that protect it work at any age.
How much should you trust it?
Treat this as an interesting finding, not a law of nature. There are good reasons for caution.
It’s a small study: 108 people, all from one part of California. Most participants weren’t followed across the whole age range, so the two peaks come from piecing together lots of shorter snapshots rather than watching anyone age from 25 to 75. Some researchers have also questioned the statistical methods used to spot the peaks, arguing they could exaggerate how sharp the changes look.
The authors say themselves that it needs repeating in larger, more varied groups. Until that happens, the honest summary is this: the evidence for ageing in bursts is intriguing but early. The evidence that midlife is a key time to look after your heart, metabolism and muscles is far older and much stronger.
So don’t book an expensive private “biological age” test because of this study. No test available to you on the high street or online can tell you whether you’re having a molecular burst, and no UK guidance recommends trying.
What should you do about ageing in your 40s and 60s?
The useful thing about the study is that it points at areas where you can already make a difference. Even the researchers suggested paying closer attention to heart health, muscle and alcohol during these years.
Get your numbers checked. In England, if you’re aged 40 to 74 and don’t already have heart disease, stroke, type 2 diabetes, kidney disease or dementia, you should be invited for a free NHS Health Check every five years. It covers blood pressure, cholesterol and your risk of heart disease, stroke and diabetes. If you haven’t been invited, ask your GP practice. Some areas also run checks through pharmacies or community venues. The NHS Health Check is an England-only programme. In Scotland, Wales and Northern Ireland, talk to your GP practice or a pharmacist about checking your blood pressure and other risk factors.
Look again at your drinking. If the mid-forties shift really does change how you process alcohol, the old routine may be doing more damage than it used to. UK guidance is not to drink more than 14 units a week on a regular basis, spread over three or more days, with several drink-free days. That’s roughly six pints of average-strength beer. It’s a limit, not a target.
Lift something heavy. Muscle markers shifted in both waves, and losing muscle with age is well documented. The UK Chief Medical Officers’ physical activity guidelines stress that every bit of movement counts and that muscle-strengthening activity matters as well as getting out of breath. Weights, resistance bands, press-ups, carrying the shopping home: it all helps, and starting at 60 is still worth it.
Watch the coffee clock. If caffeine now hits you harder or stays in your system longer, have your last cup earlier in the day and see whether you sleep better.
Mind the carbs as you near 60. The second wave involved sugar metabolism. That doesn’t mean cutting out bread. It means more fibre, fewer sugary drinks and keeping an eye on your waistline, which is a better guide to risk than the bathroom scales alone.
And if something has changed and won’t settle, such as tiredness, needing to wee more often, unexplained weight loss or chest discomfort when you exert yourself, book a GP appointment rather than putting it down to your age. Use NHS 111 for urgent advice, and call 999 if you have chest pain or other emergency symptoms.
In short
A Stanford study of 108 adults found that many molecules in the body change in two bursts, averaging around 44 and 60. The first involves how you handle fats, alcohol and caffeine, and the second involves sugar metabolism, immunity and the kidneys. The study is small and its methods have been questioned, so treat the exact ages loosely. The sensible response hasn’t changed: get your free NHS Health Check if you’re in England, drink within 14 units a week, keep your muscles working and see your GP about any change that won’t go away.
Sources
Midcent Health
Adrian Irving writes about health for men 45 and over who would rather do something than worry. Training, weight loss, sleep, cholesterol and blood tests, heart health, testosterone, the prostate, mental health and your sex life – what the evidence says, what's worth trying, and when it's time to see your GP.
One of Midcent's writers. Spotted something? Write to adrian@midcent.uk.
