Vitamin D is produced naturally by the skin in response to sunlight and may help to slow the ageing process and protect against heart disease, according to the study.

　　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 general ageing process."

　　Vitamin D made by the action of sunlight on the skin accounts for 90 per cent of the body's supply, but lower levels can also be obtained through food such as fish, eggs and breakfast cereals.

　　Other studies have suggested the vitamin plays a key role in protecting against cancer and heart disease.