. They also found a trend for benefit with occasional use.
The study, published in Melanoma Research, involved almost 500 individuals attending a dermatology clinic who reported on their use of vitamin D supplements.
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Regular users had a significant 55% reduction in the odds of having a past or present melanoma diagnosis, while occasional use was associated with a nonsignificant 46% reduction. The reduction was similar for all skin cancer types.
However, senior author Ilkka T. Harvima, MD, PhD, department of dermatology, University of Eastern Finland and Kuopio (Finland) University Hospital, warned there are limitations to the study.
Despite adjustment for several possible confounding factors, “it is still possible that some other, yet unidentified or untested, factors can still confound the present result,” he said.
Consequently, “the causal link between vitamin D and melanoma cannot be confirmed by the present results,” Dr. Harvima said in a statement.
Even if the link were to be proven, “the question about the optimal dose of oral vitamin D in order to for it to have beneficial effects remains to be answered,” he said.
“Until we know more, national intake recommendations should be followed.”
The incidence of cutaneous malignant melanoma and other skin cancers has been increasing steadily in Western populations, particularly in immunosuppressed individuals, the authors pointed out, and they attributed the rise to an increased exposure to ultraviolet radiation.
While ultraviolet radiation exposure is a well-known risk factor, “the other side of the coin is that public sun protection campaigns have led to alerts that insufficient sun exposure is a significant public health problem, resulting in insufficient vitamin D status.”
For their study, the team reviewed the records of 498 patients aged 21-79 years at a dermatology outpatient clinic who were deemed by an experienced dermatologist to be at risk of any type of skin cancer.
Among these patients, 295 individuals had a history of past or present cutaneous malignancy, with 100 diagnosed with melanoma, 213 with basal cell carcinoma, and 41 with squamous cell carcinoma. A further 70 subjects had cancer elsewhere, including breast, prostate, kidney, bladder, intestine, and blood cancers.
A subgroup of 96 patients were immunocompromised and were considered separately.
The 402 remaining patients were categorized, based on their self-reported use of oral vitamin D preparations, as nonusers (n = 99), occasional users (n = 126), and regular users (n = 177).
Regular use of vitamin D was associated with being more educated (P = .032), less frequent outdoor working (P = .003), lower tobacco pack years (P = .001), and more frequent solarium exposure (P = .002).
There was no significant association between vitamin D use and photoaging, actinic keratoses, nevi, basal or squamous cell carcinoma, body mass index, or self-estimated lifetime exposure to sunlight or sunburns.
However, there were significant associations between regular use of vitamin D and a lower incidence of melanoma and other cancer types.
There were significantly fewer individuals in the regular vitamin D use group with a past or present history of melanoma when compared with the nonuse group, at 18.1% vs. 32.3% (P = .021), or any type of skin cancer, at 62.1% vs. 74.7% (P = .027).
Multivariate logistic regression analysis revealed that regular vitamin D use was significantly associated with a reduced melanoma risk, at an odds ratio vs. nonuse of 0.447 (P = .016).
Occasional use was associated with a reduced, albeit nonsignificant, risk, with an odds ratio versus nonuse of 0.540 (P = .08).
For any type of skin cancers, regular vitamin D use was associated with an odds ratio vs. nonuse of 0.478 (P = .032), while that for occasional vitamin D use was 0.543 (P = .061).
“Somewhat similar” results were obtained when the investigators looked at the subgroup of immunocompromised individuals, although they note that “the number of subjects was low.”
The study was supported by the Cancer Center of Eastern Finland of the University of Eastern Finland, the Finnish Cancer Research Foundation, and the VTR-funding of Kuopio University Hospital. The authors report no relevant financial relationships.
A version of this article first appeared on Medscape.com.