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Health News Archive 271 - Cancer
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Raising Vitamin D Intake Cuts Cancer Risk 30%

Raising the RDA of vitamin D from 400 IU to 1500 IU could cut the number of deaths from cancer by 30 percent, say the 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.”

Vitamin D refers to two biologically inactive precursors – D3, also known as cholecalciferol, and D2, also known as ergocalciferol. Vitamin D3, produced in the skin on exposure to UVB radiation (290 to 320 nm), is said to be twice as bioactive as vitamin D2, which is derived from plants and only enters the body via the diet.  Both D3 and D2 precursors are hydroxylated in the liver and kidneys to form 25-hydroxyvitamin D (25(OH)D), the non-active ‘storage' form, and 1,25-dihydroxyvitamin D (1,25(OH)2D), the biologically active form that is tightly controlled by the body.

There is growing evidence that 1,25(OH)2D has anticancer effects, but the discovery that non-kidney cells can also hydroxylate 25(OH)D had profound implications, implying that higher 25(OH)D levels could protect against cancer in the local sites.

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.

Vitamin D levels were strongly linked to physical activity and skin color – darker skinned people produce less vitamin D on exposure to the sun, relative to fair-skinned people.  Dietary vitamin D was also a strong predictor of vitamin D levels, but supplements had only a slight effect, consistent with the common use of the less active vitamin D2 in multivitamins, say the researchers.

“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 2006 issue of the Journal of the National Cancer Institute.

The RDA of 400 International Units (IU), equal to 10 micrograms per day, raises plasma levels of 25(OH)D by a modest 7 nm/L.  “Achieving a 25(OH)D increment of 25 nm/L may require a vitamin D supplementation of at least 1500 IU per day, a safe but not generally encouraged level,” said Giovannucci.

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 William 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 biological evidence for inhibition of carcinogenesis is strong and, often, was predicted by the prior epidemiological findings on sunlight exposure.”

The vitamin's protection is proposed to be multifaceted, by reducing the formation of blood vessels in tumors (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.  An average daily dose of 1500 IU costs about $.08 per day.  Calls for raising the recommended daily allowance of the vitamin based on a growing body of science is also reaching consumers, whose awareness of these health links is increasing and outlets have reported massive boosts in sales.

Source:

Edward Giovannucci, Yan Liu, Eric B. Rimm, Bruce W. Hollis, Charles S. Fuchs, Meir J. Stampfer, Walter C. Willett; Prospective Study of Predictors of Vitamin D Status and Cancer Incidence and Mortality in Men. Journal of the National Cancer Institute, Vol. 98, No. 7, 451-459, April 5, 2006

Gary G. Schwartz and William J. Blot; Editorial: Vitamin D Status and Cancer Incidence and Mortality: Something New Under the Sun. J Natl Cancer Inst 2006; 98: 428-430.