Are You Getting Enough Vitamin D?

Article by Joel Fuhrman, M.D.

Since it’s summer time,  you might assume you will get enough vitamin D from the sun. But that is likely not the case. Vitamin D insufficiency now is thought to affect 30 to 50 percent of the world’s population.12

The main source of vitamin D for most people is the sun..

The main source of vitamin D for most people is the sun, but achieving adequate levels of vitamin D via sunlight can be difficult depending on your geographical location, skin color, and age. Even if you live in a warm climate, you may not make enough vitamin D from sunlight alone. In a study of Hawaii residents who reported an average of 29 hours of sun exposure per week, half had vitamin D levels below 30 ng/ml.3 The only way to know for sure if you’re getting enough vitamin D is to have a 25(OH)D blood test. The scientific evidence supports a favorable range of 25(OH)D levels between approximately 30 and 45 ng/ml.4-9

In addition, there is the concern that too much sun exposure can lead to skin cancer. Since it becomes difficult for most people to manage an amount of sun exposure that would achieve an optimal vitamin D status without damaging the skin, and since very few foods naturally contain vitamin D, it makes sense to supplement. Taking a vitamin D supplement is a better way to take all the guesswork out of it.

The Health Benefits of Vitamin D

There are many compelling reasons to maintain vitamin D sufficiency. The most known justification is that adequate stores of vitamin D help prevent rickets in children and osteoporosis in older adults. But, there are other critical health benefits, too.  Vitamin D insufficiency is thought to be a key contributor to many diseases, including several cancers, diabetes, cardiovascular disease, depression, and autoimmune diseases.10 If you need further evidence of how important this nutrient is, consider this: Scientists have found that vitamin D has biological actions in almost every cell and tissue in the human body.

Vitamin D Fights Cancer

More than 800 scientific papers have been published documenting the relationship between vitamin D and cancer. The most recent research suggests that vitamin D adequacy reduces the risk of death in breast, colorectal, lung, and prostate cancers, leukemia and lymphomas, and all cancers combined.11 A 2014 meta-analysis found that supplementation with vitamin D3 was associated with a reduced risk of death from cancer.12

Studies have confirmed that vitamin D can block cancer cell growth

Studies have confirmed that vitamin D can block cancer cell growth by altering the expression of genes that regulate inflammation, cell death, and cell proliferation and interfering with the growth-promoting actions of IGF-1 and other growth factors. In addition, vitamin D is linked to enhanced DNA repair and immune defenses, along with angiogenesis inhibition.1314 Today it has been well-established that maintaining an adequate vitamin D level is an effective strategy for protection against many types of cancer

How Much Vitamin D Do You Need?

I recommend taking vitamin D3 which is the  natural form of the vitamin and a higher-quality supplement compared to vitamin D2. It used to be D2 was the only vegan vitamin D supplement, but vegan D3 is now available also.

Take a consistent daily dose of vitamin D3 aiming to achieve a  25(OH)D level that is between 30 to 45 ng/ml. If you do not supplement, it makes sense to have your 25(OH)D levels tested;  be proactive about your health, because a long-standing deficiency can be harmful.

Unfortunately, many multivitamins do not contain nearly enough vitamin D to produce adequate 25(OH)D levels; some contain only 400 IU. In my experience, 2000 IU has been an appropriate daily dose to bring most people into a favorable blood range; it is a good place to start if you haven’t yet tested your 25(OH)D level But I also recommend everyone get a 25(OH)D blood test to confirm their baseline levels and guide further supplementation. Importantly, more vitamin D is not necessarily better; a 25(OH)D above approximately 45 ng/ml does not provide any further benefit and may even be detrimental.47-9

Visit for more information on the importance of Vitamin D.


Holick MF, Chen TC. Vitamin D deficiency: a worldwide problem with health consequences. Am J Clin Nutr 2008, 87:1080S-1086S.

  1. Lee JH, O’Keefe JH, Bell D, et al. Vitamin D deficiency an important, common, and easily treatable cardiovascular risk factor? J Am Coll Cardiol 2008, 52:1949-1956.
  2. Binkley N, Novotny R, Krueger D, et al. Low vitamin D status despite abundant sun exposure. J Clin Endocrinol Metab 2007, 92:2130-2135.
  3. Zittermann A, Iodice S, Pilz S, et al. Vitamin D deficiency and mortality risk in the general population: a meta-analysis of prospective cohort studies. Am J Clin Nutr 2012, 95:91-100.
  4. Schottker B, Ball D, Gellert C, Brenner H. Serum 25-hydroxyvitamin D levels and overall mortality. A systematic review and meta-analysis of prospective cohort studies. Ageing Res Rev 2013, 12:708-718.
  5. Bischoff-Ferrari HA. Vitamin D and fracture prevention. Rheum Dis Clin North Am 2012, 38:107-113.
  6. Melamed ML, Michos ED, Post W, Astor B. 25-Hydroxyvitamin D Levels and the Risk of Mortality in the General Population. Arch Intern Med 2008, 168:1629-1637.
  7. Durup D, Jorgensen HL, Christensen J, et al. A reverse J-shaped association of all-cause mortality with serum 25-hydroxyvitamin D in general practice: the CopD study. J Clin Endocrinol Metab 2012, 97:2644-2652.
  8. Sempos CT, Durazo-Arvizu RA, Dawson-Hughes B, et al. Is there a reverse J-shaped association between 25-hydroxyvitamin D and all-cause mortality? Results from the U.S. nationally representative NHANES. J Clin Endocrinol Metab 2013, 98:3001-3009.
  9. Holick MF. Sunlight and vitamin D for bone health and prevention of autoimmune diseases, cancers, and cardiovascular disease. Am J Clin Nutr 2004, 80:1678S-1688S.
  10. Grant WB, Peris AN. Differences in vitamin D status may account for unexplained disparities in cancer survival rates between African and White Americans. DermatoEndocrinology 2012, 4.
  11. Bjelakovic G, Gluud LL, Nikolova D, et al. Vitamin D supplementation for prevention of mortality in adults. Cochrane Database Syst Rev 2014, 1:CD007470.
  12. Fleet JC, DeSmet M, Johnson R, Li Y. Vitamin D and cancer: a review of molecular mechanisms. Biochem J 2012, 441:61-76.
  13. Moukayed M, Grant WB. Molecular link between vitamin D and cancer prevention. Nutrients 2013, 5:3993-4021.

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