The studies showed that patients with higher levels of the vitamin in their blood when they were diagnosed were less likely to die from their disease.

The first study, published in the British Journal of Cancer, found that in patients with colorectal cancer, those with higher blood levels of vitamin D at diagnosis were 50% less likely to die during that time than those with lower levels.

The lead researcher commented "Our study shows that levels of vitamin D after colorectal cancer diagnosis may be important for survival.

"We are now planning further research in patients with bowel cancer to see if vitamin D has the same effect, and to investigate how vitamin D works."

In the second study, UK researchers found a link between low blood levels of vitamin D and recurring malignant melanoma - the most dangerous form of skin cancer.

Patients with the lowest levels at diagnosis were 30% more likely to suffer a relapse after treatment than those with the highest levels. Patients with higher amounts of vitamin D in their blood also had thinner tumours when they were diagnosed. The findings were published in the Journal of Clinical Oncology.

Vitamin D is produced by the body in the presence of sunlight. It is also present in some foods, such as fatty fish and eggs. Vitamin D is a vital nutrient essential for many body processes and has also been linked to protecting against other conditions, including osteoporosis, diabetes, asthma, high blood pressure and depression.

Research paper details:

• K Ng, B M Wolpin, J A Meyerhardt, et al. Prospective study of predictors of vitamin D status and survival in patients with colorectal cancer. 2009 British Journal of cancer 101, 916-923.

• J A Newton Bishop, S Beswick, J Randerson-Moor, et al. Serum vitamin D levels, VDR, and survival from melanoma. Journal of Clinical Oncology, 2009 ASCO Annual Meeting Proceedings. Vol 27, No 15S (May 20 Supplement), 2009.