Healthy levels of vitamin D may help to slow the ageing process and protect against age-related diseases, a team of British scientists has found. The claim follows a study of more than 2,000 women which found that those with the lowest vitamin D levels showed the greatest signs of biological ageing.

Scientists at King's College London who conducted the study said large-scale trials were needed to confirm the discovery, but if proved correct the finding could have a dramatic impact on healthcare.

In summer much of the vitamin D we need is created by a reaction in the skin powered by sunlight. In the darker winter months vitamin D comes largely from food such as cod liver oil and mackerel.

The team, led by Brent Richards, an endocrinologist, recorded vitamin D levels in 2,160 women aged 18-79. The scientists then took white blood cells and examined them for genetic signs of ageing.

Among the most reliable measures of a person's age are telomeres, the lengths of genetic material that cap the free ends of DNA in a cell. With age, the telomeres shorten and the DNA becomes more unstable until eventually the cell dies. For the experiment the women were organised into three groups according to their vitamin D levels. The study found that those with the highest vitamin levels had significantly longer telomeres - equivalent to five years of normal ageing - than those showing the lowest vitamin D scores.

Dr Richards, whose study was published yesterday in the American Journal of Clinical Nutrition, 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 explain how vitamin D has a protective effect on many ageing-related diseases, such as heart disease and cancer. What's interesting is that there's a huge body of evidence that shows sunshine ages your skin - but it also increases your vitamin D levels. So, like many times in medicine, we find there's a trade-off."

Tim Spector, a co-author of the paper, 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."

Health guidelines on vitamin D recommend a daily intake of between 200 and 600 international units (IU), with the higher level required by the over-70s. An 85g tin of tuna contains roughly 200 IU of vitamin D. Maximum healthy levels of vitamin D range from 1,000 IU for young children to 2,000 IU for adults. Too much leads to toxicity, which can cause nausea, weakness and kidney damage.

Previous studies have suggested that vitamin D may help moderate the immune system and so aid the treatment of immune-related disorders such as rheumatoid arthritis and type one diabetes.