Women who develop breast cancer are more likely to survive the disease if they have high levels of vitamin D in their blood, a new study has found.

Vitamin D is known to be essential for healthy bones, but is present in very few foods. It is also known as the sunshine vitamin because it is made in the body when the ultralviolet rays from sunlight strike the skin.

However, Ireland's northerly latitude and lack of winter sunlight means that Irish people often cannot make enough of the vitamin in this way. As a result, some people choose to take supplements.

US scientists decided to look at the possible relationship between breast cancer survival rates and 25-hydroxyvitamin D, which is a metabolite (product of metabolism) produced by the body following the ingestion of vitamin D.

They analysed five studies on this topic, which involved almost 4,500 breast cancer patients.

The study found that patients with high levels of the vitamin in their blood were twice as likely to survive the disease compared to those with low levels.

Women with high levels were found to have an average of 30 nanograms per millileter (ng/ml) of 25-hydroxyvitamin D in their blood. Those with low levels had an average of 17 ng/ml.

"Vitamin D metabolites increase communication between cells by switching on a protein that blocks aggressive cell division. As long as vitamin D receptors are present, tumour growth is prevented and kept from expanding its blood supply. Vitamin D receptors are not lost until a tumour is very advanced. This is the reason for better survival in patients whose vitamin D blood levels are high," the scientists noted.

They said that while further studies are required to confirm these results, doctors should consider adding vitamin D to a patient's standard care.

"There is no compelling reason to wait for further studies to incorporate vitamin D supplements into standard care regimens since a safe dose of vitamin D needed to achieve high serum levels above 30 ng/ml has already been established," they insisted.

Details of these findings are published in the journal, Anticancer Research.