"We have quantitated the ability of adequate amounts of vitamin D to prevent all types of invasive cancer combined,which had been terra incognita until publication of this paper," said Cedric Garland, professor at the University of California, San Diego.

Researchers made the first connection between vitamin D deficiency and some cancers in 1980 when they noted populations at higher latitudes (with less available sunlight) were more likely to be deficient in vitamin D, which is produced by the body through exposure to sunshine, and experience higher rates of colon cancer.

Subsequent studies found vitamin D links to other cancers, such as breast, lung and bladder.

The new study sought to determine what blood level of vitamin D was required to effectively reduce cancer risk.

The marker of vitamin D was 25-hydroxyvitamin D or 25(OH)D, the main form in the blood.

The researchers pooled analyses of two previous studies of different types - a randomised clinical trial of 1,169 women and a prospective cohort study of 1,135 women.

By combining the two studies, the researchers obtained a larger sample size and a greater range of blood serum levels of 25(OH)D.

The only accurate measure of vitamin D levels in a person is a blood test. In the clinical trial cohort, the median blood serum level of 25(OH)D was 30 nanogrammes per millilitre (ng/ml). In the prospective cohort, it was 48 ng/ml.

Garland does not identify a singular, optimum daily intake of vitamin D or the manner of intake, which may be sunlight exposure, diet and/or supplementation.

He said the current study simply clarifies that reduced cancer risk becomes measurable at 40 ng/ml, with additional benefit at higher levels.

The research was published in the journal PLOS ONE.

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