People with higher levels of vitamin D appear to have a higher risk of developing NMSC (nonmelanoma skin cancer), researchers from Henry Ford Hospital, Detroit, reported in Archives of Dermatology. However, as higher UV (ultraviolet) radiation exposure general results in greater levels of vitamin D, the relationship is “complicated”.

Nonmelanoma skin cancers (NMSC) usually start in either squamous cells or basal cells – located at the base of the outer layer of the skin, or they cover the internal and external surfaces of the body. They usually develop on sun-exposed parts of the body, such as the backs of the hands, lips, neck, ears, or face. They can be either fast or slow growing, depending on their type – however, they do not generally spread to other parts of the body. They are generally easy to cure if detected and treated early.

The authors explained that more NMSC cases are diagnosed annually in the USA than breast, colorectal, lung, prostate and ovarian cancer put together.

Previous studies have found a compelling link between sunlight exposure and skin cancer, with UV being the main risk factor for NMSC.

Even though exposing the skin to UV-B triggers the body’s production of vitamin C, the researchers explain that “evidence of the association of vitamin D levels with skin cancer has been inconsistent,” especially the link between nonmelanoma skin cancer and circulating serum vitamin D levels.

Some studies indicate that vitamin D could lower BCC (basal cell carcinoma) risk, the most common NMSC subtype; SCC (squamous cell carcinoma) is another type. The investigators wanted to find out more about a possible link between vitamin D serum levels and the risk of SCC and BCC.

Melody J. Eide, M.D., M.P.H., and team carried out a study on 3,223 Caucasian members of an HMO (health maintenance organization) who were at high risk of developing NMSC.

The participants received low-bone density or osteoporosis counseling between 1997 through 2001 – they were followed up for an average period of 9.8 years. Their assessment included levels of serum 25-hydroxyvitamin D (25-OHD), calcium, and creatinine. 25-OHD indicates vitamin D levels. The HMO claims database included cases of both BCC and SCC nonmelanoma skin cancers.

Over two-thirds of them had inadequate vitamin D levels. 240 of them had a diagnosis of NMSC (49 SCC and 163 BCC, and 28 with both forms).

Participants whose vitamin D levels were adequate had a higher risk of developing NMSC, even when other risk factor were taken into account.

Even though there was a positive link between 25-OHD levels and NMSC, there was not a statistically significantly higher risk in developing tumors in other parts of the body, such as the legs, trunk, or arms, for those exposed to UV radiation.

The scientists say that their findings contribute “to the limited and conflicting epidemiological investigation regarding the relationship between vitamin D and NMSC.”

The authors concluded:

“An increased baseline serum 25-OHD level was significantly associated with an increased NMSC risk. This association was positive, though non-significant on less UV-exposed body sites, and UV exposure remains a likely confounder. The complex and confounded relationship of vitamin D, UV, and NMSC makes classic epidemiological investigation difficult in the absence of carefully measured history of cumulative UV exposure.”

Written by Christian Nordqvist