Drinking skimmed milk instead of semi-skimmed milk may add more than four years to your biological age, a study suggests.
Thousands of people had their DNA analysed for signs of ageing and gave details about their diet.
For every one per cent increase in milk fat content, DNA aged the equivalent of more than four years.
It suggests those who drink red-topped milk, around 0.3 per cent fat, have considerably better longevity than drinkers of blue-top milk, which has 3.6 per cent fat.
The scientists behind the study believe saturated fat in milk puts stress on cells, fuelling damage and tissue death.
But they cannot prove their findings – that skimmed milk can prevent your DNA from ageing – because the study was merely observational.
Drinking skimmed milk instead of semi-skimmed milk may add more than four years to your biological age, a study suggests
Study leader Professor Larry Tucker said: ‘It was surprising how strong the difference was high-fat milk, you should be aware that doing so is predictive of or related to some significant consequences.’
The research was on 5,834 American adults who answered questionnaires about their milk consumption.
Scientists at Brigham Young University, Utah, looked at biological age, which is a representation of how much damage has accumulated in various cells and tissues in the body.
To do this, they looked at the length of telomeres, which are found at the ends of each of our chromosomes, which carry our DNA.
They act in a similar way to the plastic bits on the ends of shoelaces, preventing the chromosomes from fraying.
As we age, these telomeres become shorter, our DNA becomes unstable and its ability to produce healthily youthful tissues diminishes.
Although chronological age is the key factor accounting for the length of telomeres, other things contribute significantly, particularly our lifestyle.
For example, a smoker would have shorter telomeres than a non-smoker because the toxins in cigarettes cause cellular damage.
Researchers said for every one per cent increase in milk fat consumed, telomeres were 69 base pairs shorter in the adults studied.
This translated to four additional years of biological ageing, based on the fact each additional year of chronological age in the present sample was associated with telomeres that were 15.3 base pairs shorter.
Just under a third of the adults reported consuming full-fat (whole) milk and another 30 percent reported drinking two per cent milk.
One in ten people consumed one per cent milk and another 17 per cent drank non-fat milk. About 13 per cent did not drink any cows’ milk at all.
Nearly half of the people in the study consumed milk daily and another quarter consumed milk at least weekly.
Professor Tucker said: ‘Milk is probably the most controversial food in our country.
‘If someone asked me to put together a presentation on the value of drinking milk, I could put together a 1-hour presentation that would knock your socks off. You’d think, “Whoa, everybody should be drinking more milk”.
‘If someone said do the opposite, I could also do that. At the very least, the findings of this study are definitely worth pondering. Maybe there’s something here that requires a little more attention.’
Surprisingly, the research also found people who did not drink any milk lived longer than those who consumed low-fat milk.
Professor Tucker said the study findings provide support for the current dietary guidelines which encourage adults to consume low-fat milk, both nonfat and one per cent milk, and not high-fat milk, as part of a healthy diet.
He said: ‘It’s not a bad thing to drink milk. You should just be more aware of what type of milk you are drinking.’
The findings are published in the science journal Oxidative Medicine and Cellular Longevity.