Vitamin D
What is Vitamin D?
Historically humans obtained ~80% of their vitamin D requirement via sunlight exposure to the skin, with the remaining ~20% coming from dietary intake. (1) However, modern living habits have reduced skin exposure to the sun, and very few non-fortified foods we now consume contain significant amounts of vitamin D. (2) Because of this lifestyle shift a large proportion of the general population is vitamin D deficient, with observational studies finding ~40% of Europeans to be deficient and ~13% severely deficient. (3)
Vitamin D is essential for maintaining bone health and muscular function, it helps to protect against cognitive decline, and supports our immune system. (4) Adequate intake of vitamin D has also been correlated with increased resistance and reduced severity of Covid-19, however human clinical studies are still lacking. (5)
Are you Deficient?
People most at risk of vitamin D deficiency include:
Those who have limited direct sunlight exposure or always use sunblock when exposed
People with darker skin
Those over 50 years of age
Unfortunately vitamin D status can only be determined via blood draw, with the serum (blood) concentration of its 25- hydroxylated (25-(OH)D) form the common marker measured. (6)
Table 1. National Health and Medical Research Council (NHMRC) vitamin D deficiency classification for both adult men and women
How much to take?
Ideally you should test your vitamin D serum concentration, and then take appropriate action based on this result, however this is not always practical, and could also burden an already strained health care system. (7)
A review article published in the European Journal of Clinical Nutrition (2020) gave the below recommendation for the safe and effective supplementation of vitamin D without the need for monitoring. (3)
Suggested Dosage = 25 μg of vitamin D3 (1000 IU) per day
The Australian Government (NHMRC) cautions against excessive dosing of vitamin D due to some research linking atherosclerosis with large doses of this vitamin, below is their upper level (maximum dose) recommendation.
Upper level of intake = 80 μg of vitamin D3 (3200 IU) per day
Key Points
Adequate intake of vitamin D is essential for optimal health and immune function
There is a high chance you are not getting enough from sun exposure and dietary intake
Ideally you would get your current vitamin D levels checked before supplementing
In the absence of testing the suggested dosage is 25 μg of vitamin D3 (1000 IU) per day
Don’t start supplementing with vitamin D before discussing with your family doctor
Don’t exceed the suggested dosage unless instructed by a registered health physician
References
1. Sassi F, Tamone C, D’Amelio P. Vitamin D: Nutrient, Hormone, and Immunomodulator. Nutrients. 2018;10(11):1656.
2. MacDonell SO, Miller JC, Harper MJ, Waters DL, Houghton LA. Vitamin D status and its predictors in New Zealand aged-care residents eligible for a government-funded universal vitamin D supplementation programme. Public Health Nutrition. 2016;19(18):3349-60.
3. Amrein K, Scherkl M, Hoffmann M, Neuwersch-Sommeregger S, Köstenberger M, Tmava Berisha A, et al. Vitamin D deficiency 2.0: an update on the current status worldwide. European Journal of Clinical Nutrition. 2020;74(11):1498-513.
4. De La Puente Yagüe M, Collado Yurrita L, Ciudad Cabañas MJ, Cuadrado Cenzual MA. Role of Vitamin D in Athletes and Their Performance: Current Concepts and New Trends. Nutrients. 2020;12(2):579.
5. Grant WB, Lahore H, McDonnell SL, Baggerly CA, French CB, Aliano JL, et al. Evidence that Vitamin D Supplementation Could Reduce Risk of Influenza and COVID-19 Infections and Deaths. Nutrients. 2020;12(4):988.
6. Dirks NF, Ackermans MT, Lips P, De Jongh RT, Vervloet MG, De Jonge R, et al. The When, What & How of Measuring Vitamin D Metabolism in Clinical Medicine. Nutrients. 2018;10(4):482.
7. Dobson R, Cock HR, Brex P, Giovannoni G. Vitamin D supplementation. Practical Neurology. 2018;18(1):35-42.