For some time, scientists have theorized that vitamin D may be an effective agent against a number of different types of cancer.

A recent study in the Journal of the National Cancer Institute looked at circulating vitamin D levels and colorectal cancer. The researchers examined 7,107 control subjects and 5,706 colorectal cancer subjects with a wide range of circulating vitamin D levels.

Compared to those who had a lower range of sufficiency for bone health — 20 ng/mL to 25 ng/mL — subjects with vitamin D levels less than 12 ng/ mL (deficiency) had a 31 percent higher risk of colorectal cancer. The reduced risk was greater in women than men.

People with higher vitamin D levels also were found to have a lower risk of colorectal cancer.

Interestingly, vitamin D levels greater than 40 ng/mL were not associated with a significantly decreased colorectal cancer risk.

The authors concluded, “Higher circulating [vitamin D] was related to a statistically significant, substantially lower colorectal cancer risk in women and nonstatistically significant lower risk in men.”

Vitamin D is produced in the skin and in the kidneys. In the skin, production is stimulated by exposure to ultraviolet light from the sun.

Vitamin D deficiency is very common, especially in climates farther from the Earth’s equator, where ultraviolet light declines through the fall and winter months.

I recommend vitamin D to all my patients during the fall and winter seasons. A daily dose of 2,000 IU to 6,000 IU is perfectly safe to take unless you have kidney problems. And I often suggest more when a patient is acutely ill — though vitamin D can be over-supplemented because it is fat-soluble.

If you are supplementing with vitamin D, I suggest using the natural form: vitamin D3 (cholecalciferol). Avoid the synthetic form: vitamin D2 (ergocalciferol).

If your doctor tries to prescribe you the synthetic form, find a new doctor.