Vitamin-D supplements to protect against cancer

Zosia Chustecka

January 17, 2006

Jan 17, 2006

San Diego, CA - If the advice to take vitamin-D supplements to prevent osteoporosis isn't enough to convince patients to do so, accumulating evidence showing a protective effect against cancer may help to tip the argument. In fact, in view of the increasing data showing a link between vitamin-D deficiency and an increased risk of certain cancers (colon, breast, prostate, and ovarian) and in view of the high prevalence of vitamin-D deficiency in the US, researchers argue the case for taking vitamin-D supplements to protect against cancer in a paper published online before print December 27, 2005 in the American Journal of Public Health [ 1 ].

Vitamin D is considered deficient?with respect to osteoporosis?when serum levels of 25(0H)D fall below 15¿to 20¿ng/mL, but the review points out that levels below 30¿ng/mL have been associated with an increased risk of colon cancer. In two studies, the risk of colon cancer was doubled at this level.

Vitamin-D deficiency may account for several thousand premature deaths from cancers annually, it says. "The preponderance of evidence, from the best observational studies the medical world has to offer, gathered over 25 years, has lead to the conclusion that public-health action is needed," lead author Dr Cedric Garland (University of California, San Diego) comments in a prepared statement. "Primary prevention of these cancers has largely been neglected, but we now have proof that the incidence of colon, breast, and ovarian cancer can be reduced dramatically by increasing the public's intake of vitamin D."

Garland and colleagues recommend a daily intake of 1000¿IU of vitamin D, which is half the safe upper intake established by the US National Academy of Sciences. This would be consistent with maintaining a serum 25(OH)D level at or above 30¿ng/mL in most people, they comment. Doses of up to 1000¿IU/day "have no reasonable likelihood of producing toxicity," they add, noting that reports of vitamin-D toxicity in the past resulted from massive doses (50¿000¿to 150¿000¿IU/day) on a long-term basis.

However, the National Academy of Sciences itself currently recommends much lower levels: 200¿IU/day for those aged 1 to 50 years, 400¿IU for those aged 50 to 70 years, and 600¿IU for those over the age of 71.

The authors comment that the easiest way to reach the proposed target of 1000¿IU/day is through food and supplements, which would cost about five cents a day. To achieve this level of intake through diet alone is difficult (for example, a glass of milk has 100¿IU), and the other source of vitamin D, sun exposure, "has its own concerns and limitations," they comment. Because the safety of this dose has been "thoroughly assessed and the benefits found so far in observational studies are considerable, expanded use of vitamin D as a public-health measure should not be delayed," the authors comment.


Blacks have more vitamin-D deficiency and more cancer

Vitamin-D deficiency is particularly high among black Americans, the review notes. One survey found a severe deficiency (levels below 15¿ng/mL) in 42% of black women; another study found that blacks on average had vitamin-D levels that were half those found in whites. People with dark skin pigmentation are less able to synthesize vitamin D from sunshine, and blacks need about twice the amount of sun exposure to make the same amount of vitamin D.

The review also points out that cancer statistics are much worse in blacks than in whites?colon cancer has a 19% higher incidence and 33% higher mortality rates, breast cancer mortality rates are 28% higher (although the incidence rates are slightly lower), and prostate cancer has mortality rates that are double and an incidence rate that is 1.6 times higher. These higher rates remain even after adjustment for socioeconomic status and access to care, and the authors attribute the substantially lower survival rates in blacks to their decreased ability to synthesize vitamin D.

"Long-term studies have demonstrated the efficacy of moderate intake of vitamin D in reducing cancer risk and, when administered with calcium, in reducing the incidence of fractures," Garland et al comment. "Despite these reassuring studies, the public-health and medical communities have not adopted vitamin D for cancer prevention." They argue that they now should do so, and they look to "leadership from the public-health community" to provide the best hope for action.

Source

  1. Garland CF, Garland FC, Gorham ED, et al. The role of vitamin D in cancer prevention. Am J Public Health 2006; DOI: 10.2105/AJPH.2004.045260. Available at http://www.ajph.org/.

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