In 1980, scientists realized that colon cancer death rates in the United States decreased with latitude. Outdoor workers have now been found to have a lower risk of developing prostate cancer less than indoor workers. Breast cancer mortality rates vary by sunlight exposure. So what’s the connection between sunlight and lower cancer rates? Vitamin D!    

   Can a vitamin really affect the genetics of your body? Yes, biologically speaking, it can. Interestingly, we find vitamin D receptors in tissue from brain, prostate, breast, and colon, and also on immune cells. These tissues and cells have been found to respond to the active form of vitamin D (1,25-(OH)₂D) and subsequently, change their regulation of genes as a result of this vitamin. In other words, vitamin D-responsive genes exist in the cells of certain organs. The presence (or absence) of vitamin D can increase (or decrease) the amount of genes and proteins produced in our bodies.     While the role of vitamin D in cancer prevention has yet to be established, results of studies look promising.   

   Colon Cancer

   Interestingly, the geographic distribution of colon cancer mortality resembles the historical geographic distribution of rickets[i], suggesting that decreased sunlight exposure and diminished vitamin D nutritional status may be related to increased risk colon cancer risk. More recent studies have reported that higher vitamin D intakes and serum 25(OH)D levels are associated with reductions in colorectal cancer risk.[ii] To date, there are about 25 to 30 studies showing a beneficial effect of vitamin D on colon cancer. Although the Women’s Health Initiative study of Ca/Vitamin did not show a benefit, results suggested that low serum vitamin D (in its prevalent form, 25(OH)D was related to increased colon cancer risk. A meta-analysis of 5 studies showed that those in the highest quintile of vitamin D intake (>33ng/ml) had 50% reduction in colon cancer.[iii] The study concluded that, with the evidence to date, daily intake of 1000-2000 IU/day of vitamin D(3) could reduce the incidence of colorectal with minimal risk.   

   Prostate Cancer   

   Fourteen out of 26 epidemiological studies of prostate cancer and vitamin D show a protective effect. Specifically, these studies demonstrate correlations between risk factors for prostate cancer and conditions that can result in decreased vitamin D levels[iv]. “Increased age is associated with an increased risk of prostate cancer, as well as with decreased sun exposure and decreased capacity to synthesize vitamin D. The incidence of prostate cancer is higher in African American men than in white American men, and the high melanin content of dark skin is known to reduce the efficiency of vitamin D synthesis. Geographically, mortality from prostate cancer is inversely associated with the availability of sunlight.”[v] However, more prospective studies are needed to confirm a significant relationship between serum 25(OH)D levels, the prevalent form of vitamin D in our bodies, and the subsequent risk of developing prostate cancer. A prospective study of Finnish men offers promising results, as the investigators found that low serum 25(OH)D levels were associated with earlier and more aggressive prostate cancer development[vi]. Further research is needed to determine the nature of the relationship between vitamin D nutritional status and prostate cancer risk.    

   Breast Cancer   

   Breast cancer mortality also follows a similar geographic distribution to that of colon cancer.[vii] However, direct evidence of an association between vitamin D nutritional status and breast cancer risk is limited. The first National Health and Nutrition Examination Survey (NHANES I), a prospective study, found that several measures of sunlight exposure and dietary vitamin D intake were associated with a reduced risk of breast cancer in the female participants 20 years later[viii]. More recently, a 16-year study of more than 88,000 women found that higher intakes of vitamin D were associated with significantly lower breast cancer risk in premenopausal women.[ix] Results of a pooled, dose-response analysis of two case-control studies of women with breast cancer showed that women with breast cancer had significantly lower plasma 25(OH)D levels compared to controls.[x] Garland et al., the authors of the study, reported that women with a 25(OH)D level of 52 ng/ml (130 nmol/L) experienced a 50% lower risk of developing breast cancer compared to women with 25(OH)D levels lower than 13 ng/mL (32.5 nmol/L)[xi]. Apparently, biologically active forms of vitamin D can inhibit the growth of breast cancer cells. However, according to Garland et al., around 4,000 IU of vitamin D₃ would need to be consumed daily, or 2,000 IU of vitamin D₃ daily plus very moderate sun exposure, to obtain a 25(OH)D level of 52 ng/mL.[xii] The current tolerable upper limit of intake for adults, set by the Food and Nutrition Board of the Institute of Medicine, is 2,000 IU/day. Overall, 9 out of 13 studies reported a favorable association of vitamin D intake with 50% reduction in breast cancer risk.   

   Bottom Line   

   In general, further research is needed to firmly conclude the positive role of vitamin D in preventing cancer. Results of some, but not all, human epidemiological studies suggest that vitamin D may protect against various cancers. However, it is important to note that epidemiological studies cannot prove such associations. For those at risk of colon, prostate, or breast cancer, you might want to make sure you are receiving at least an adequate daily intake of 400 IU, or 10 micrograms, although “a recent dose-response analysis estimated that 1,000 IU of oral vitamin D daily would lower one's risk of colorectal cancer by 50%”[xiii] so 400 IU might not be enough to have a positive effect.    

   Where to find Vitamin D: Food Sources   

   Good sources of vitamin D: Fish (herring, salmon, halibut), cod liver oil, shiitake mushrooms. You might want to avoid cod liver oil as a source of vitamin D, however, because of the high retinol content, which can affect skeletal health. Other foods are fortified with vitamin D, which means vitamin D is added to them, including oatmeal, milk (cow, rice, soy), orange juice, yogurt, cereal, eggs, and egg beaters. The following chart is adapted from the Linus Pauling Institute at Oregon State University, Micronutrient Information Center website:[xiv]

    Forms of vitamin D    

   Vitamin D comes in two forms as calciferols, a group of chemicals related to vitamin D. Cholecalciferol, or D3, is the form in animal foods and supplements. 10 ug cholecalciferol is equivalent to 400 IU of vitamin D. Our bodies can also use sunlight to convert a compound in our skin to cholecalciferol. Cholecalciferol is converted to another form in the liver, and then again in the kidney to become the active form of vitamin D in our bodies.    

   Final Note   

   There is a huge potential role of vitamin D in not only lowering mortality rates for cancer, but also in decreasing mortality rates of cardiovascular disease and diabetes mellitus. Our bodies need this fat-soluble vitamin to survive and to carry out daily physiological functions. Be sure to maintain an adequate intake of vitamin D-rich foods to potentially lower your risk of certain diseases, but do not exceed the established upper limit of 2000 IU/day!