Over the next two decades, researchers predict new cases of cancer will increase to 22 million annually throughout the globe. Meanwhile, in the United States alone, scientists estimate more than 1.68 million new diagnoses and nearly 600,000 deaths will occur in 2016. What can slow this malignant spread? A new UC San Diego School of Medicine study focusing exclusively on women suggests the sunshine vitamin could apply the brakes.

Higher levels of vitamin D in the blood is associated with a reduced risk of cancer, the researchers said. Specifically, women over the age of 55 whose 25-hydroxyvitamin D blood concentrations were 40 nanograms per milliliter (ng/ml) or higher showed a 67 percent lower risk of cancer than those with levels of 20 ng/ml or less.

The Sunshine Vitamin

Your body naturally produces vitamin D through exposure to sunshine. Yet, your ability to metabolize and use vitamin D depends on several processes within your body. First, the liver must convert vitamin D to a chemical known as 25-hydroxyvitamin D, and from there, the kidneys must transform 25-hydroxyvitamin D into its active form.

As we get older, though, our bodies may become less efficient at making the active form of vitamin D. Other physiological factors, including skin type, may also affect how much usable D our bodies make. Despite getting enough sunlight, many people may be vitamin D deficient.

It is well known that populations in higher latitudes are more likely to be deficient in vitamin D. In fact, 35 years ago Dr. Cedric Garland, adjunct professor and member of Moores Cancer Center, and his late brother Frank, observed a higher number of deaths due to colon cancer in locations with less sunlight. At this time, they made the connection between vitamin D deficiency and cancer. Subsequent studies by the Garland brothers linked the vitamin to specific cancers, including breast and prostate.

While vitamin D’s protective effects are clear, Garland wanted to know the precise blood levels required to reduce risk. For the current investigation, Garland and his co-researchers began with an analysis of two separate and distinct studies from the past. The first included 1,169 women over the age of 55, the second 1,135 women in the same age range; both studies monitored vitamin D blood levels in relation to cancer incidence. To measure how much of this vitamin was circulating in their blood, the women performed and recorded the results of 25-hydroxyvitamin D tests, a common standard used by doctors.

Pooling and analyzing data from the two studies, Garland and his colleagues compared the incidence of cancer (with the exception of non-melanoma skin cancer) as it related to each woman’s vitamin D concentrations over a period of about 3.9 years.

Immediately, they discovered lower cancer incidence among women with higher levels of vitamin D. After adjusting for cofactors, such as smoking and age, the researchers found women with concentration levels greater than or equal to 40 ng/ml had a 67 percent decreased risk of cancer compared to women with levels less than 20 ng/ml.

Naturally, since only women participated in these studies, the results cannot be generalized to other groups. Nevertheless, Garland and his team hope to conduct future investigations of vitamin D to determine possible protective effects.

“Prevention of cancer, rather than solely expanding early detection or improving treatment, will be essential for reversing the current upward trend of cancer incidence worldwide,” concluded the researchers. They added that their new analysis suggests vitamin D might serve as a crucial prevention tool.

Source: McDonnell SL, Baggerly C, French CB, et al. Serum 25-Hydroxyvitamin D Concentrations ≥40 ng/ml Are Associated with >65% Lower Cancer Risk: Pooled Analysis of Randomized Trial and Prospective Cohort Study. PLOS One. 2016.