Tropic of Cancer

Sun Exposure, Vitamin D, and Cancer

“A closer study of the action of solar radiation on the body might well reveal the nature of cancer immunity.”

That quote – from Dr. Frank Apperly – comes from a 1941 study in which Dr. Apperly analyzed North American cancer statistics and found that people who live nearer the equator generally have lower risk of developing various cancers, including breast, lung, prostate, and colon cancers.

Over the 65 years since Dr. Apperly’s groundbreaking research, a closer study of the action of solar radiation on the body has revealed that the mechanism by which human skin converts sunlight into vitamin D is, literally, a life saver. And this is illustrated, once again, in a new breast cancer study from the Imperial College of London (ICL).

Testing the levels

Previous studies have shown that vitamin D deficiency is linked to greater risk of breast cancer. The ICL study was designed to clarify the relationship between vitamin D levels and the progression of breast cancer from early to advanced stages.


  • Blood samples were taken from 204 women with early stage malignancy, nearly 280 women with invasive breast cancer, and 75 women with advanced breast cancer
  • In patients with early stage breast cancer, vitamin D levels were significantly higher compared to both of the other groups
  • In patients with early stage breast cancer, levels of parathyroid hormone (PTH) were significantly lower compared to both of the other groups (PTH is typically overproduced when breast cancer is metastasized to bone)

Lead author of the study, Dr. Carlo Palmieri, told NutraIngredients-USA that researchers need to examine the implications of monitoring vitamin D levels in breast cancer patients and the importance of maintaining high levels of the vitamin.

D is for daylight

The ICL study raises a question: Do higher vitamin D levels prevent the progression of breast cancer, or does the cancer somehow lower blood levels of the vitamin?

Beyond the fact that Dr. Apperly demonstrated many decades ago that high levels of the vitamin are linked to lower breast cancer risk, we also have two previous studies that support the preventive effect of vitamin D on this cancer.

In the first study, more than a thousand healthy women and about 560 women with breast cancer completed dietary and lifestyle interviews with researchers at Mount Sinai Hospital in Toronto. Analysis of the data showed that women who had the highest vitamin D intake (through extended sunlight exposure, or intake of cod liver oil or milk) between the ages of 10 and 29 had a 40 percent reduced risk of developing breast cancer later in life compared to women with the lowest D intake. Researchers believe that high vitamin D levels during the years when breast tissue is in rapid development may help protect the breasts from cancer.

In the second study, researchers at the University of California, San Diego, tested blood samples in more than 1,750 women. Subjects who had blood levels of 52 nanograms per milliliter of D had a 50 percent reduced risk of developing breast cancer compared to women with low D levels. The UCSD team noted that in order to reach 52 ng/mL requires a vitamin D intake of about 1,000 IU daily – a level that is difficult to reach without daily sun exposure.

The best dietary sources of vitamin D are eggs, liver, fish liver oils, and oily fish such as salmon, sardines, trout, and tuna. Fish oil supplements are a good source of vitamin D, but talk to your doctor before adding these supplements to your regimen.

“Serum 25 Hydroxyvitamin D Levels in Early and Advanced Breast Cancer” Journal of Clinical Pathology, Published Online 10/17/06,
“Vitamin D Levels Linked to Breast Cancer Progression” Stephen Daniells, NutraIngredients-USA, 10/17/06,