As many as 50 percent of breast and colon cancer cases could be prevented by increasing intake of vitamin D, according to a study that backs continued calls for higher vitamin D upper limits.
Published in the August 2007 supplement of the journal, Nutrition Reviews, researchers at the University of California, San Diego (UCSD) compiled data from observational studies showing an inverse link between serum 25-hydroxyvitamin D [25(OH)D] and these cancers. They took previous results one step further by looking into the dose-response gradient between serum 25 (OH)D and the risk of both cancers.
The findings confirm what industry and researchers have long been advocating: that the public does not consume enough vitamin D and vitamin D needs to be made more available to consumers through public awareness and increased upper limits.
According to the study's projections, in North America, a 50 percent reduction in colon cancer incidence would require universal intake of 2000 IU (International Units) per day of vitamin D, and a 50 percent reduction in breast cancer would require intake of 3500 IU per day.
"These gradients for cancer risk suggest that the upper limit should be revised upward, since there is a considerable benefit, and no established adverse effect of vitamin D3 intake below 10,000 IU/d," wrote the study authors.
Deficiency in vitamin D affects inhabitants of colder climates, because sunlight induces synthesis of vitamin D in humans. As such, if a consumer is not getting adequate exposure to the sun for vitamin D and its subsequent impact on their serum 25 (OH)D levels, they should be supplementing with vitamin D. In adults, vitamin D deficiency can lead to osteopenia, osteoporosis, muscle weakness, fractures, common cancers, autoimmune diseases, infectious diseases and cardiovascular diseases.
According to the study, the median adult intake of vitamin D in the US is only 230 IU per day, versus the researchers' recommended 2000 IU per day. In addition, they called into question the type of vitamin D used. "Use of ergocalciferol (vitamin D2), which is popular in Europe and is used in some major [inexpensive] US brands of multivitamins, should be discontinued immediately in favor of vitamin D3."
Vitamin D refers to two biologically inactive precursors - D3, also known as cholecalciferol, and D2, also known as ergocalciferol. Vitamin D-3 is produced in the skin on exposure to UVB radiation (290 to 320 nm), and is 10 times more bioactive. Vitamin D-2 is derived from plants and only enters the body via the diet.
The UCSD School of Medicine study extrapolated dose-response curves based on age-standardized incidence rate estimates for 177 countries in 2002 from the International Agency for Research on Cancer (IARC) Globocan database. The researchers obtained serum 25 (OH)D levels for each country via previous studies as well as winter solar ultraviolet B irradiance by country from NASA (US' National Aeronautics and Space Administration) data.
With universal attainment of a serum 25 (OH)D level of ≥ 55 ng/ml, the researchers predict that in North America at least 60,000 cases of colorectal cancer could be avoided per year and another 85,000 cases of breast cancer.
Garland, Cedric F. et al. "What is the dose-response relationship between vitamin D and cancer risk?" Nutrition Reviews 65;8 (Suppl):91-95.