• drhsmithcp

Reach for fish at the grocery, open up your sunroof, and pick up a vitamin D3 supplement.

Updated: Jun 8

written by: Houston Smith, DC

Vitamin D is needed for hundreds of functions in our bodies including cell growth, repair, various biochemical reactions, bone density, and bone remodeling.

Vitamin D has also been proven to lower the incidence of colorectal cancer among other types of cancer. In one study by Gorham ED et al. they showed that

>33 ng/mL blood levels of vitamin D reduced the incidence of colorectal cancer by 50% compared to <12 ng/mL. Research from Heaney RP et al. suggests a serum concentration greater than 40 ng/L may be required to achieve the effects in bone health, cancer protection, and neuromuscular function.

Achieving a level of 40ng/mL of vitamin D can be challenging if dietary sources are not consumed daily. Dairy fortified with vitamin D, salmon, swordfish, tuna, egg yolks, and cod are great sources of vitamin D. The cheapest way to get vitamin D is to expose yourself to enough sunlight daily. Exposing 40-60% of your skin to sunlight daily for 3 or more hours combined with dietary sources and supplementation are a great way to achieve that 40ng/mL threshold. Daily supplementation of 1000-2000 IUs would help meet that vitamin D goal and provide health benefits in bone, gut, and cell function. Supplementation of up to 10,000IUs per day are recognized as safe for most people, however talk to your primary care physician before starting a high dosage.

Remember to take in vitamin D from different sources because sun exposure alone may not be enough to achieve the 40ng/mL threshold needed for significant health benefits. Research from Binkley et al. suggests there are variations among individuals and how they synthesize vitamin D from the sun. They found the upper limit of vitamin D absorption from abundant sun exposure to be 60ng/mL. Abundant sun exposure in this study was defined as 3+ hours or more per day 5 days a week for 3 months. If you are not getting outside close to this every single day, chances are your blood levels of vitamin D are much lower than 40ng/mL. Supplementation, along with sun exposure and healthy dietary choices are necessary to achieve optimal levels of vitamin D.


  1. Heaney RP, Davies KM, Chen TC, et al. Human serum 25-hydroxycholecalciferol response to extended oral dosing with cholecalciferol. AM K Clin Nutr. 2003; 77:204-210

  2. Binkley N, Novotny R, Krueger D, Kawahara T, Daida YG, Lensmeyer G, Hollis BW, Drezner MK. Low vitamin D status despite abundant sun exposure. J Clin Endocrinol Metab. 2007

  3. Gorham ED, Garland CF, Garland FC, Grant WB, Mohr SB, Lipkin M, Newmark HL, Giovannucci E, Wei M, Holick MF. Optimal vitamin D status for colorectal cancer prevention: a quantitative meta analysis. Am J Prev Med. 2007

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