A STUDY of wild sheep living on a remote Scottish island has added to growing evidence that the "sunshine vitamin" - vitamin D - improves fertility.

Scientists from the University of Edinburgh found that sheep with higher levels of vitamin D in their blood at the end of the summer had more lambs the following spring.

The researchers studied an unmanaged population of Soay sheep on St Kilda in the Outer Hebrides, where sheep have lived wild for thousands of years.

It is hoped the research will help other mammals, including humans. Vitamin D is produced in the skin of sheep and many other animals, including humans, after exposure to sunlight.

Many studies have linked vitamin D to reproductive health in animals and humans but this study is the first evidence of the link in wild animals.

Dr Richard Mellanby, head of small animal medicine at the university's Royal (Dick) School of Veterinary Studies, who led the research, said: "Our study is the first to link vitamin D status and reproductive success in a wild animal population.

"Examining the non-skeletal health benefits of vitamin D in humans is challenging because people are exposed to different amounts of sunlight each day.

"Studying the relationship between skin and dietary sources of vitamin D - and long-term health outcomes - is more straightforward in sheep living on a small island."

Low levels of vitamin D have previously been linked to a range of medical conditions, including multiple sclerosis. A lack of the so-called sunshine vitamin has long been linked to Scotland's high rate of MS, with a dearth of natural sunlight thought to be partly to blame.

Last summer, an advisory body set up by the UK Government recommended that all Scots should take vitamin D supplements because of the health implications of a lack of bright sunshine.

The independent Scientific Advisory Body on Nutrition (SACN) said the bleak British weather is stopping much of the population from receiving healthy amounts of the essential vitamin from sunlight - and natural food sources alone are not enough to boost levels.

It made the recommendation after studying the links between vitamin D levels and a range of health problems, including musculoskeletal health, heart disease, type 1 diabetes, cancer and multiple sclerosis.

Government advice is that at-risk groups, including pregnant women, children up to the age of five, adults over 65, and people with darker skin as well those who do not expose their skin to sunlight, should take a daily vitamin D supplement.

A separate study out last year also found that a lack of the vitamin almost halves the chances of conceiving for women undergoing IVF treatment.

Researchers in Italy looked at the success rates of assisted fertility procedures in 154 women who were deficient in the vitamin and 181 with sufficient levels in their blood. The second group was nearly twice as likely to conceive as the first.

The latest research was published in the journal Scientific Reports.