MONTREAL, May 7 -- Increased vitamin D intake is not protective
against melanoma, and may actually increase the risk, according to the
results of the largest prospective cohort study on the topic.
Among the 68,611 participants in the Vitamins and Cohort Lifestyle (VITAL)
study, there was no evidence of an association between overall supplement
use or duration of use with either an increased or decreased risk of
melanoma, Maryam Asgari, M.D., from Kaiser Permanente in Oakland, Calif.,
reported at the Society of Investigative Dermatology meeting here.
Similarly, 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=0.05).
"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. Asgari.
"When we looked at diet alone there was a slightly increased risk," she said
in an interview, "but when we combined diet and supplement use, the risk
washed out."
"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
high amounts of fatty fish, liver, and egg yolk."
The VITAL cohort had an average age of 62, and was 52% female.
Dr. Asgari and colleagues used a food frequency questionnaire to determine
dietary intake of vitamin D and other nutrients in the preceding year. They
also collected data about vitamin supplement use over the preceding 10
years.
Total vitamin D intake from both dietary and supplemental sources was then
calculated for a 10-year period and compared with incident melanoma cases
from the SEER (Surveillance, Epidemiology and End Results) database.
Despite the lack of association in overall supplement use and melanoma, the
researchers did find a nonsignificant trend towards a protective effect at
the higher supplement doses (P=0.67).
But, Dr. Asgari acknowledged that the study "did not have a lot of high dose
supplement users -- most of them were taking an additional 600 IU."
Not measuring sun exposure or vitamin D levels were other limitations of the
study, according to the investigators.
Dr. Asgari noted their findings are "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 melanoma in
women, but not 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 2004; 13: 1042-51).
"Vitamin D and skin cancer risk has been a really hot topic lately," said
Dr. Asgari. "There's a whole lot of new evidence showing our vitamin D
levels are probably insufficient, and vitamin D insufficiency may be linked
with certain cancer risk. But the overall take-home message of our study is
that vitamin D is not associated with decreased melanoma risk."
Source : National Institutes of Health
