Vitamin D, produced naturally by the skin in response to sunlight, may help to slow the ageing process, according to scientists.
And the "sunshine vitamin" may also help protect against age-related diseases, such as heart disease.
Researchers from King's College London studied 2,160 women aged between 18 and 79, looking at their telomeres - a biological marker of ageing found in DNA.
As people get older their telomeres get shorter and they become more susceptible to certain illnesses.
But the study found women with high levels of vitamin D had comparatively longer telomeres - a sign of being biologically younger and healthier.
The study suggests vitamin D may help to slow down the ageing process of DNA, and therefore the ageing process as a whole.
Lead researcher Dr Brent Richards said: "These results are exciting because they demonstrate for the first time that people who have higher levels of vitamin D may age more slowly than people with lower levels of vitamin D.
"This could help to explain how vitamin D has a protective effect on many ageing related diseases, such as heart disease and cancer." He said further studies are required to confirm the findings.
Professor Tim Spector, head of KCL's twin research unit, and a co-author of the report, added: "Although it might sound absurd, it's possible that the same sunshine which may increase our risk of skin cancer may also have a healthy effect on the ageing process in general."

The November 2007 issue of Scientific American has an article on sunlight, vitamin D, and health. The conclusion is that vitamin D and sunlight improve health.

Excessive sunlight does damage skin. But according to the article, a light skinned woman in a bikini will gain 10,000 units of vitamin D in 10 to 15 minutes of sunlight. More exposure time does not increase the amount. So you don't need much time in the sun. And the skin's protective anti-oxidant systems are protective for about 45 minutes in sunlight.