The reviewers suggest that adults should daily take 2,000 international units (IU) of vitamin D -- in a form called vitamin D3 (cholecalciferol) -- to help prevent some cancers, including colon cancer and breast cancer.
But that's not a prescription or a guarantee. The review is based on observational studies, which didn't directly test vitamin D for cancer prevention.
The 2,000-IU daily dose of vitamin D suggested by the reviewers is currently considered the "tolerable upper limit" for vitamin D, according to the National Academy of Sciences' Institute of Medicine (IOM).
The IOM hasn't set a "recommended intake" for vitamin D. But it has previously determined that "adequate intake" of vitamin D is 200 IU per day for the first 50 years of life, 400 IU per day from 51-70, and 600 IU per day after age 71.
Vitamin D and Cancer Review
The new research review on vitamin D and cancer comes from scientists including Cedric Garland, DrPH, of the University of California at San Diego's family and preventive medicine department.
They cite 29 observational studies in their report, which appears in the journal Nutrition Reviews.
Garland and colleagues combined data from the observational studies. They conclude that in North America, "a projected 50% reduction in colon cancer incidence would require a universal intake of 2,000 IU per day of vitamin D3."
"A similar reduction in breast cancer incidence would require 3,500 IU per day," write the reviewers, cautioning that such a dose exceeds the Institute of Medicine's tolerable upper limit for vitamin D.
Vitamin D may help prevent cancer in several ways, including maintaining healthy cells with normal life spans, discouraging out-of-control cell reproduction, and hindering the formation of new blood vessels for tumors, according to the reviewers.
Vitamin D doesn't just come in supplements. It's also found in some foods -- including salmon, tuna, and some fortified dairy products and cereals.