MONTREAL — Increased vitamin D intake is not protective against melanoma, according to the results of the largest prospective cohort study on the topic.
“If you're worried about melanoma risk, I don't think popping a vitamin D pill is going to help, at least in the standard doses,” said Dr. Maryam M. Asgari, of Kaiser Permanente in Oakland, Calif.
In fact, her study, presented at the annual meeting of the Society for Investigative Dermatology, actually suggests a trend toward a greater risk of melanoma with high dietary intake of vitamin D.
“When we looked at diet alone there was a slightly increased risk, but when we combined diet and supplement use, the risk washed out,” she said in an interview. “It's hard to say whether this was an effect of dietary vitamin D itself, or something else—for example, mercury—in the diets of people who consume large amounts of fatty fish, liver, and egg yolk.”
The study included a cohort of 68,611 participants in the Vitamins and Cohort Lifestyle (VITAL) study (J. Invest. Dermatol. 2009;129:1675-80). The average age of the cohort was 62 years, and 52% of participants were female.
A food frequency questionnaire was used to determine dietary intake of vitamin D and other nutrients in the preceding year. Data were also collected about vitamin supplement use over the past 10 years. Total vitamin D intake from both dietary and supplemental sources was then calculated for a 10-year period, compared with incident melanoma cases from the Surveillance, Epidemiology, and End Results database.
There was no evidence of an association between overall supplement use or duration of use with either an increased or decreased risk of melanoma, Dr. Asgari reported. However, there was a nonsignificant trend toward a protective effect at the higher supplement doses (P = .67). “In our study, we did not have a lot of high-dose supplement users. Most of them were taking an additional 600 IU,” she commented.
When supplement use was examined in combination with dietary intake, there was no association with melanoma risk. However, high dietary intake alone was associated with a slightly increased risk of melanoma (P = .05).
“These people were just eating their normal diet, but this finding is not inconsistent with what's been published in the past, with regard to cohort studies,” she said. Specifically, a Norwegian study of almost 51,000 participants found that cod liver oil consumption was associated with an increased risk of melanoma in women, but not in men (Int. J. Cancer 1997;71:600-4).
In contrast, one case-control study of around 1,000 participants found a protective effect of high dietary vitamin D intake, but no impact when dietary and supplemental intake were examined together (Cancer Epidemiol. Biomarkers Prev. 2004;13:1042-51).
“The overall take-home message of our study is that vitamin D is not associated with decreased melanoma risk,” Dr. Asgari said.
'If you're worried about melanoma risk, I don't think popping a vitamin D pill is going to help.' DR. ASGARI