More than three-fourths of people with a variety of cancers have low levels of vitamin D, and the lowest levels are associated with more advanced cancers, a new study suggests.

High-dose supplements increased vitamin D levels to normal in most patients studied, but it is too soon to know if supplementation improved their outlook, says researcher Thomas Churilla, MS, a third-year medical student at Commonwealth Medical College in Scranton, Penn.

The findings were presented here at the annual meeting of the American Society for Radiation Oncology (ASTRO).

Vitamin D and Cancer Risk

Vitamin D is found in some foods, especially fatty fish, milk, and fortified cereals. Vitamin D is also obtained by exposure to sunlight.

Some studies have suggested a link between low vitamin D levels and cancer risk and progression, but others have not. None has proven cause and effect.

Research in the laboratory suggests that vitamin D has anti-tumor properties, regulating genes involved in the multiplication and spread of cancer cells, Churilla tells WebMD.

For the study, the researchers collected blood samples from 160 men and women with cancer and measured their levels of vitamin D. The five most common diagnoses were breast, prostate, lung, thyroid, and colorectal cancers.

Among people in the study, 42% had vitamin D insufficiency, defined as levels between 20 and 30 nanograms per milliliter (ng/mL) of blood. An additional 32% had vitamin D deficiency, with levels less than 20 ng/mL.

Vitamin D Levels and Stage III Cancer

The average level of vitamin D was about 24 ng/mL. People with levels below 24 ng/mL were nearly three times more likely to have stage III cancer than those with higher vitamin D levels.

Criteria for different stages differ by type of cancer. But in general, stage III indicates more extensive disease than lower stages: larger tumor size and/or spread of the cancer beyond the organ in which it first developed to nearby lymph nodes and/or adjacent organs.

There was no association between low vitamin D levels and even more advanced, stage IV cancers that have spread throughout the body, however. Churilla says that could be because patients with stage IV cancers may have already been seen by a variety of doctors who treated them for vitamin D deficiency.

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