MONDAY, Aug. 15 (HealthDay News) -- The higher a person's
vitamin D levels, the higher the risk of non-melanoma skin cancer,
such as basal cell carcinoma and squamous cell carcinoma, finds new
But the study, appearing in the Aug. 15 issue of the
Archives of Dermatology, stops short of saying that high vitamin D levels might actually cause these types of cancer, the most common malignancies in the United States.
And because ultraviolet (UV) radiation exposure is necessary for
vitamin D production in the body, it might simply mean that people
with more sun exposure tend to develop more non-melanoma skin
cancers. It's unclear whether it's the damage from UV rays that
accounts for the risk, or rising vitamin D levels that accompany
exposure to the rays.
"This adds to the murky water [surrounding the relationship between vitamin D and skin cancer]," said Dr. Vijay Trisal, assistant professor of surgical oncology at City of Hope Cancer Center in Duarte, Calif. "Is it vitamin D or sun exposure? The two go hand-in-hand."
Other scientists have investigated a possible relationship
between vitamin D and skin cancer, but so far the results have been
limited and conflicting.
One study suggested that higher vitamin D levels might actually
protect against skin cancer. This could be because vitamin D may
inhibit a pathway involved in cancer, said Dr. Melody Eide, a
dermatologist with Henry Ford Hospital in Detroit, and lead author
of the current study.
But two other studies had results suggesting the opposite.
Eide and colleagues based their findings on 3,223 mostly female,
white patients in a Detroit health maintenance organization who had
visited a doctor either because they had osteoporosis or low bone
Many more patients (2,257) had too-low levels of vitamin D than
had adequate levels (966).
Over a follow-up period of almost 10 years, 163 participants
developed basal cell carcinoma, 49 developed squamous cell
carcinoma, and 28 developed both.
Those with vitamin D levels above a certain threshold had a 70
percent greater risk of developing one of these cancers. (That
threshold was 15 nanograms per milliliter; people with less than
that were considered deficient in vitamin D.)
People with higher vitamin D levels also tended to develop their
skin cancer on parts of the body not typically exposed to sunlight,
like the arms and legs, but that finding was not statistically
significant, the researchers reported.
At this research stage, it's difficult to untangle the possible
mechanisms behind this.
"It's a triangular relationship between UV light with the production of Vitamin D and the induction of skin cancer," Eide said. "That makes it difficult to know."
The study didn't take into account lifetime sun exposure, family
history of skin cancer, vitamin D supplementation, exercise,
smoking or several other factors that might have influenced the
outcome of the study. In addition, the study authors noted that it
was "highly likely" that the participants' exposure to sunlight
might have skewed the results.
"We need some measure of lifetime cumulative UV exposure, which is very difficult to measure," Eide said. "We tend to move around a lot; people go on vacations. There could be critical windows during our life."
The Skin Cancer Foundation has more on all forms of