Raising vitamin D intake could cut risk of many cancers

Raising the RDA of vitamin D from 400 IU to 1500 IU could cut the number of deaths from cancer by 30 per cent, say the US scientists investigating the link between vitamin D levels and cancer risk.

The link between vitamin D intake and protection from cancer dates from the 1940s when Frank Apperly demonstrated a link between latitude and deaths from cancer, and suggested that sunlight gave “a relative cancer immunity.”

The Health Professionals Follow-Up study, a prospective study of over 50,000 US male health professionals, is the first study to examine total cancer incidence and factors that determine 25(OH)D levels.

The research, led by Edward Giovannucci from Harvard School of Public Health, used data from 1095 participants who had plasma 25(OH)D levels measured, and then computer-predicted levels for the whole cohort.

The scientists then linked the 25(OH)D levels to determinants of vitamin D exposure, like dietary and supplemental vitamin D, geographical residence, skin pigmentation and leisure-time activity.

Vitamin D levels were strongly linked to physical activity and skin colour – darker skinned people produce less vitamin D on exposure to the sun, relative to fair-skinned people.

“In this cohort analysis, a 25(OH)D increment of 25 nanomoles per litre (nm/L) was associated with a 17 per cent reduction in total cancer incidence, a 29 per cent reduction in total cancer mortality, and a 45 per cent reduction in mortality of digestive-system cancer,” wrote Giovannucci in the April issue of the Journal of the National Cancer Institute (vol. 98, pp. 451-459).

The best source of vitamin D is from sun exposure, with a fair-skinned person estimated to produce up to 20,000 IU after 20-30 minutes in the sun. However, sun exposure is discouraged due to the risk of skin cancer.

In an accompanying editorial, Gary Schwartz from Wake Forest University and Willian Blot from the Vanderbilt University Medical Center said clinical trials of high dose vitamin D supplementation and the risk of cancer should be “undertaken speedily”.

Schwartz and Blot said that the cohort results were likely to boost enthusiasm for the vitamin for cancer prevention, but cautioned that observational epidemiological studies had limitations that should not be overlooked.

The vitamin's protection is proposed to be multifaceted, by reducing the formation of blood vessels in tumours (angiogenesis), stimulating the mutual adherence of cells, and enhancing intercellular communication through gap junctions. All this adds up to stop proliferation of cancerous cells by contact inhibition.

Sara Hiom, head of health information at Cancer Research UK, said that the study was one of the most robust that suggested an association between low vitamin D levels and an increased risk of cancer incidence and mortality in men.

"The authors suggest that it may be wise to review daily recommended doses of vitamin D as these may currently be too low. As the sun is also an important source of the vitamin, Cancer Research UK's SunSmart campaign will continue to advise safe enjoyment of the sun without burning," she said.

Bonnie - this adds to the promising body of research linking vitamin D to reducing the risk of cancer. Although, before we raise the RDA levels to 1500 IU, there must be more research and it should be made explicitly clear that vitamin D should not be taken over the RDA unless supervised by a licensed health professional.