It is estimated that over 50 million adults in the United States either have or are at risk of developing, osteoporosis.1
Vitamin D is a fat-soluble vitamin your body makes after exposure to ultraviolet (UV) rays from the sun. It then sends a message to the intestines to increase the absorption of calcium and phosphorus, helping to form and maintain strong bones.
Deficiency has been linked to a higher incidence of osteoporosis-related bone fractures in postmenopausal women and older adults.2-3
Because of limited access to sun exposure, supplementation is the only option for most Americans to assure Vitamin D adequacy. Also, many prefer to avoid damage to the skin from excess sun exposure, including wrinkling, age spots, and skin cancer.
If using a supplement, D3 is recommended over D2. Vitamin D3 is the natural form of the vitamin made by the body in response to sunlight. D3 is also a more biologically active form of the vitamin. In a review of 56 trials of vitamin D supplementation, vitamin D3 was found to decrease mortality risk, however D2 was not.4
Vitamin D is known to have protective effects on bone health and also has several other critical functions. Vitamin D insufficiency is a key contributor to many human diseases including several cancers, diabetes, cardiovascular disease, depression, cognitive decline, and autoimmune diseases.3,5-7
Some of the most groundbreaking findings in nutrition science in recent years have been evidence of the powerful protection provided by vitamin D against common cancers: About 75 percent of women with breast cancer are vitamin D deficient.4
A 2009 meta-analysis of 19 studies established a strong inverse relationship between circulating vitamin D levels and breast cancer women in the highest vitamin D range reduced their risk of breast cancer by 45 percent.8 A 2009 review of 25 studies found that sufficient vitamin D levels were consistently associated with reduced risk of colorectal cancer.9 Even after diagnosis with colorectal cancer, higher vitamin D levels are associated with reduced risk of death.10
Cancers of the prostate, pancreas, lung, and endometrium are also associated with vitamin D insufficiency.5,11
Can you get too much vitamin D? More of a vitamin is not necessarily better. Some concerns have been raised about vitamin D supplementation, arising from studies of excessively large doses given all at once, whether D2 or D3.12,13 For comparison, the tolerable upper limit (the maximum recommended daily dose) is only 4000 IU.
One possible explanation of these negative effects is that the excessively large dose of vitamin D could have stimulated rapid bone turnover, resulting in the breakdown of existing bone.14
Not all studies on high dose vitamin D showed negative effects.15 However, a recent meta-analysis pooled all the conflicting data, and concluded that high dose vitamin D supplementation had no effect on fracture risk but slightly increased the risk of falls.16
A moderate, consistent daily dose of D3 is a safe and conservative method to keep vitamin D levels in a healthy range, not too high and not too low.
For most people, the principal source of vitamin D is production by the skin in response to sunlight. Very few foods naturally contain vitamin D, and achieving adequate vitamin D levels via sunlight can be difficult depending on your geographical location, skin color, and opportunities for sun exposure, especially in the winter months.
Plus, sun exposure to assure optimal Vitamin D status may damage and age the skin increasing wrinkling, mottling and the risk of skin cancer. A smart option is a moderate daily dose of vitamin D3, not too much or too little.
We should aim for the sweet spot of blood 25(OH)D to be between 30 to 45 ng/ml, as suggested by the scientific evidence.17-22
We should choose D3, the natural form of the vitamin, the form the body produces in response to sunlight. There is overwhelming evidence of benefit, and no risks noted in a reasonable dose.
Ingest a moderate daily dose of supplemental vitamin D3 (approximately 2000 IU/day) to reach the 30-45 ng/ml window. If you do not supplement, it makes sense to have your 25(OH)D levels tested because a long-standing deficiency can be harmful.

Dr. Fuhrman is a #1 New York Times best-selling author and a board certified family physician specializing in lifestyle and nutritional medicine. The Eat To Live Cookbook offers over 200 unique disease-fighting delicious recipes and his newest book, The End of Heart Disease, offers a detailed plan to prevent and reverse heart disease using a nutrient-dense, plant-rich (NDPR) eating style. Visit his informative website at DrFuhrman.com. Submit your questions and comments about this column directly to [email protected]