In recent years, Vitamin D, the sunshine vitamin, has been touted with keeping our bones and teeth strong while protecting against such diseases as multiple sclerosis, heart disease, diabetes, and more. Well, there’s another protective characteristic we can add to the Vitamin D list of what’s-healthy-for-us: recent studies suggest vitamin D may lower the risk of developing colorectal cancer, especially in women. Since 42% of American adults are vitamin D deficient and since that vitamin appears to prevent a whole universe of chronic diseases, we need to pay more attention to our intake of this multipurpose miracle-working vitamin.

Colorectal cancer

Colorectal cancer is the third most common cancer and third leading cause of cancer-related deaths in the United States. And there’s troubling evidence that the number of young adults diagnosed with the disease is on the rise. In response to all this evidence, the American Cancer Society recently recommended their colorectal screening be lowered from 50 years old to 45. And the Institute of Medicine increased their daily recommended dosage of vitamin D from 600 IU per day to 4,000 IU per day. But other experts disagree and feel we may need around 7,000 IU per day to truly reap the largest benefits. Not many of us could sunbathe long enough each day to get these results; plus, that great degree of exposure would leave us at risk for skin cancer.

The study

Published in the Journal of the National Cancer Institute in June, the large international study provides the strongest evidence yet that vitamin D may be protective against colorectal cancer and conversely, a deficiency in the vitamin, may increase the risk of that cancer. The study collected findings from17 previous studies and included 12,813 adults throughout the United States, Europe, and Asia.

“For both men and women, deficient levels of vitamin D were associated with a 30 percent increased risk of colorectal cancer,” says Marji McCullough, a nutritional epidemiologist with the American Cancer Society and study co-author. In the study, 5, 706 of those 12,813, had colorectal cancer and 7,107 of similar ages and race, didn’t have cancer. In addition, women’s menopausal status was taken into account. The researchers also tried to establish risk factors like smoking, low physical activity, and a high body mass index. Then, they looked at participants’ blood samples collected in the years before their cancer diagnosis to establish what role vitamin D might be playing.

The most provocative finding of the study was the strong correlation between higher blood levels of vitamin D and a lower risk of colorectal cancer in women but McCullough says researchers aren’t sure why. According to her, one hypothesis is that there is some interaction between vitamin D and female hormones. Or it’s possible vitamin D prevents cancer by reducing the proliferation of tumor cells or by stopping their growth and “actually killing those cells.”

McCullough further offered the interesting observation that beyond a certain blood level, increasingly higher amounts of vitamin D had no additional benefit. In short, more isn’t better. In fact, overdoing it can be toxic and can cause kidney stones. So, talk with your healthcare provider and have your blood levels checked. Different individuals have different vitamin D needs.


1. Does Vitamin D Really Protect Against Colorectal Cancer? NPR Radio.

2. Circulating Vitamin D and Colorectal Cancer Risk: An International Pooling Project of 17 Cohorts. Journal of the Nation Cancer Institute. 14 June 2018.