Research utilizing combined data from 17 studies that included more than 12,000 people from the U.S., Europe, and Asia found that optimal levels of vitamin D for colon cancer prevention are higher than the current U.S. recommendation of 600 international units (IU) per day.
Humans make 90 percent of our vitamin D naturally from sunlight exposure to our skin — specifically, from ultraviolet B exposure to the skin, which naturally initiates the conversion of cholesterol in the skin to vitamin D3.
Theories linking vitamin D deficiency to certain cancers have been tested and confirmed in more than 200 epidemiological studies, and understanding of its physiological basis stems from more than 2,500 laboratory studies, according to epidemiologist Cedric Garland, DrPH, professor of family and preventive medicine at the UC San Diego School of Medicine.
“This is the number one chemopreventive substance on the planet and its natural without side effects.”
Higher blood concentrations of vitamin D are linked to a lower risk of colorectal cancer, especially in women, according to the large new study from researchers at Harvard T.H. Chan School of Public Health, the National Cancer Institute, the American Cancer Society, and 20 other medical centers and organizations around the world.
They concluded that “optimal” levels of the vitamin for colorectal cancer prevention are greater than those recommended by the National Academies of Sciences, Engineering and Medicine, which are based only on bone health.
How much vitamin D people should get has been a subject of controversy for years. Authors of the new paper said one problem with past studies was substantial differences in the tests used to measure 25-hydroxyvitamin D, the most widely accepted measure of the vitamin’s concentration in the blood.
The few previous randomized trials on vitamin D supplements and colorectal cancer didn’t show an effect, perhaps because of their size or compliance issues, the authors said.
The new study addressed many of the gaps and problems of earlier studies, according to Smith-Warner. It used a single, widely accepted test for vitamin D measurements and standardized the data that already existed.
Both D3 and D2 precursors are hydroxylated in the liver and kidneys to form 25- hydroxyvitamin D (25(OH)D), the non-active ‘storage’ form, and 1,25-dihydroxyvitamin D (1,25(OH)2D), the biologically active form that is tightly controlled by the body.
There is growing evidence that 1,25(OH)2D has anticancer effects, but the discovery that non-kidney cells can also hydroxylate 25(OH)D had profound implications, implying that higher 25(OH)D levels could protect against cancer in the local sites.
People with blood vitamin D levels above the recommended concentrations had a 22% lower risk of getting colorectal cancer, although it’s unclear what the optimal level of vitamin D might be for reducing the risk.
Colorectal cancer kills more than 50,000 people a year in the U.S. It’s the third most common cancer and the third leading cause of cancer-related deaths in the U.S..