Interesting article. Not necessarily unexpected as those that have a lot of sun exposure have high Vitamin D levels. Multiply the serum levels by approximately 2.5x to get Australia units.
Higher levels of vitamin D, still within the normal range, are associated with an increased risk of nonmelanoma skin cancer, researchers reported.
In a cohort study, people with higher serum 25-hydroxyvitamin D (25(OH)D) were more likely to develop squamous cell or basal cell carcinoma, according to Melody Eide, MD, and colleagues at Henry Ford Hospital in Detroit.
But other factors – such as increased exposure to sunlight – probably complicate the relationship, Eide and colleagues reported online in Archives of Dermatology.
Ultraviolet B light is known to cause skin cancer, but it also increases cutaneous vitamin D synthesis, the researchers noted, adding that the relationship between vitamin D and skin cancer is complex and studies have yielded conflicting results.
Indeed, some research suggests that vitamin D might reduce the risk of basal cell carcinoma, but other studies have had the opposite outcome.
To help clarify the situation, Eide and colleagues analyzed data, over an average of 9.8 years of follow-up, from 3,223 white members of a health maintenance organization who had a high probability of developing nonmelanoma skin cancer.
The participants had sought counseling for osteoporosis or low bone density between January 1997 and December 2001, and their assessment included levels of serum 25(OH)D, a marker for vitamin D intake and storage.
The researchers used the HMO’s claims database to track incident cases of basal cell and squamous cell carcinoma.
When they were assessed, 2,257 participants did not have a sufficient vitamin D level, where sufficient was defined as at least 30 nanograms of 25(OH)D per milliliter of serum.
All told, the researchers found, 240 patients developed nonmelanoma skin cancer, including 49 with squamous cell carcinoma, 163 with basal cell carcinoma, and 28 with both. Most cases — some 80% — occurred in sites frequently exposed to the sun.
When patients were divided into four groups according to their 25(OH)D levels, there was a trend linking the higher levels and skin cancer risk that was significant atP=0.02.
Compared with the lowest quartile, the highest (less than 19 nanograms per milliliter versus 31 or higher) had an odds ratio for cancer of 1.6 (95% CI 1.1 to 2.3), Eide and colleagues found. Intermediate quartiles also had elevated risks, but they did not reach significance compared with the lowest quartile.
Logistic regression analysis found that having a vitamin D level that was just above the cutoff for deficiency – less than 15 nanograms of 25(OH)D per mL of serum – was associated with an increased risk of nonmelanoma skin cancer. Specifically:
- For both types combined, the adjusted odds ratio was 1.8 (95% CI 1.1 to 2.9,P<0.05).
- For squamous cell carcinoma alone, the odds ratio was 1.7, but it did not reach significance with a 95% confidence interval from 0.7 to 4.0.
- For basal cell carcinoma, the odds ratio was also 1.7 but reached significance at P<0.05 (95% CI 1.00 to 2.9).
The findings add “to the limited and conflicting epidemiological investigation regarding the relationship between vitamin D and [nonmelanoma skin cancer],” Eide and colleagues concluded.
They added that, aside from UVB light, the finding might also be confounded by such things as participants’ vitamin D levels over a lifetime and consumption of vitamin D supplements, which they were unable to investigate.
Eide and colleagues also cautioned that the study was conducted at a single institution and that people who seek counseling for osteoporosis risk represent a self-selected group that may not be a representative population