What You Should Know About Vitamin D
Updated: Mar 20
Written by Stephanie Deppe, M.D.
The importance of vitamin D as a preventative for many health issues, including severe COVID-19 infection, has been well established. Just to name a few–in one study of older women with blood vitamin D levels higher than 40 ng/ml, there was a 67% reduced risk of developing all types of cancer as compared to women with levels lower than 20 ng/ml (1). In another large study that tracked deaths in over 365,000 participants over 8.9 years, higher levels of vitamin D were associated with reduced risk of all-cause mortality and deaths from cardiovascular disease or cancer. Specifically, vitamin D levels higher than 60 nmol/L and 45 nmol/L were protective against deaths from cardiovascular disease and cancer, respectively (2).
Low vitamin D levels are also associated with an increased risk of severe disease and death from COVID-19 infection (3, 4). This is true even after adjusting for other COVID-19 risk factors, including obesity, diabetes, and age (3, 4, 5). In a study published in PLOS ONE, researchers analyzed data from 1,176 patients admitted to a hospital in Israel between April 2020 and February 2021 (5). Of these, 253 patients had vitamin D levels on record within the previous two years. Researchers found a striking association between vitamin D and COVID-19 severity and death. Patients with vitamin D deficiency (<20 ng/ml) were 14 times more likely to have severe or critical disease than those with levels >40 ng/ml. Furthermore, the mortality rate was 25.6% in those with vitamin D deficiency, whereas it was only 2.3% in patients with levels of 30 ng/ml or higher.
Data from Grassroots Health–a non-profit, vitamin D research organization–suggests that the optimal level of vitamin D for health and disease prevention is between 60 ng/mL and 80 ng/mL, while the cutoff for sufficiency appears to be around 40 ng/mL (6). Many studies have used very low cut-offs for deficiency, and even these show that a significant percentage of people are deficient (7) . I feel comfortable saying that most people do not have optimal levels of vitamin D. I check vitamin D levels routinely in my patients here in Minnesota, and the vast majority are lacking in adequate vitamin D. Individuals with inadequate dietary intake, inflammatory bowel conditions, or inadequate sun exposure are at higher risk for deficiency.
Natural food sources of vitamin D are highest in fatty fish, cod liver oil, and beef liver. Eggs, fortified cereal, and milk also contain vitamin D. However, most people don’t eat enough food-rich sources to achieve adequate levels. Sunlight is nature’s solution to this problem. When our skin is exposed to sunlight, our body converts cholesterol in the skin into vitamin D, which then circulates to the liver and kidney to be converted into an active form for use. Excess vitamin D is stored in fat to be used in the future should circulating levels become insufficient (8). Sadly, most of us don’t have the luxury to sunbathe regularly or often enough to optimize vitamin D levels, which is why supplementation is often required. Vitamin D3 (cholecalciferol) is the preferred form, as it raises serum levels more effectively than D2 (9).
So, what do you do if you cannot achieve adequate levels through diet or sunlight alone? And what role do B vitamins, zinc, and vitamin K play in relationship to vitamin D? Below are some points to consider:
Make sure your test was accurate if you were taking a biotin supplement/B complex. If you are taking high doses of biotin (vitamin B7), you may receive a falsely high vitamin D result. This is because biotin can interfere with accurate test interpretation by immunoassays–a commonly used lab test (10, 11). Either stop biotin and retest, or ask your physician to check levels via LC-MS/MS (liquid chromatography – mass spectrometry), which is an accurate way to analyze 25 (OH) D. You can get a home test kit for $79.00 at Grassroots Health. https://daction.grassrootshealth.net/product/vitamin-d-home-test-kit/
Supplement with vitamin D3 if needed. It’s best to take your supplement with a meal as vitamin D is better absorbed with fats. Your dose will depend on your current levels. If you have a recent test, Grassroots Health offers a vitamin D calculator to help you determine your required dosage. Vitamin D*calculator™ - GrassrootsHealth Make sure you have your levels rechecked after about three months.
The intake of other nutrients has been shown to affect vitamin D absorption and function. Magnesium is a necessary vitamin D cofactor (see below), and vitamin K and zinc play critical roles in regulating the impact of vitamin D on bone health (12, 13, 14). Without sufficient levels of other nutrients, you won’t maximize the benefits of vitamin D supplementation. For this reason, I recommend that everyone take a high-quality multivitamin in addition to eating a healthy diet.
Get enough magnesium. The enzymes in the liver and kidneys that regulate the conversion of vitamin D into its active form (calcitriol) are dependent on magnesium to function (14). For this reason, it’s important to attain adequate dietary levels of magnesium or to supplement with magnesium. Individuals with advanced kidney disease should discuss with their physician before supplementing.
In addition to magnesium, you should also get enough vitamin K. Vitamin K is important for bone and cardiovascular health by regulating calcium. While vitamin D increases calcium absorption in the gut, vitamin K directs where the calcium goes. Vitamin K2 plays a vital role in osteoblast function (cells that help build bones), and seems to keep calcium from depositing in arteries–a major risk factor for heart disease (15). In fact, research has shown that high doses of vitamin K2 supplementation in individuals with osteoporosis reduced future fracture incidence. Furthermore, the Rotterdam Heart Study, which tracked 4,800 patients over 7 years, demonstrated that those people who had the highest quantities of dietary vitamin K2 experienced a greater than 50% reduction in deaths related to heart disease than people with the least (15).
You can get K2 from grass fed dairy or fermented foods like miso, natto or fermented vegetables. The optimal dose for supplementation is controversial, but there is no known toxic upper dose limit (16). That said, you should not supplement with vitamin K if you are on blood thinners or have disorders involving blood coagulation, such as severe liver disease. Ideally, everyone would obtain enough K2 from dietary sources, and also by maintaining a healthy gut environment through a plant-rich diet and probiotics (as gut bacteria actually make K2 as well).
Given the enormous research supporting vitamin D’s role in protecting against cancer, heart disease, severe COVID-19, osteoporosis (and several other diseases not addressed in this article), it’s a no-brainer to assess your levels and optimize your intake to maximize your health.
To your health,
McDonnell SL, Baggerly C, French CB, Baggerly LL, Garland CF, Gorham ED, et al. Serum 25-Hydroxyvitamin D Concentrations ≥40 ng/ml Are Associated with >65% Lower Cancer Risk: Pooled Analysis of Randomized Trial and Prospective Cohort Study. Slominski AT, editor. PLOS ONE. 2016 Apr 6;11(4):e0152441.
Fan X, Wang J, Song M, Giovannucci EL, Ma H, Jin G, et al. Vitamin D Status and Risk of All-Cause and Cause-Specific Mortality in a Large Cohort: Results From the UK Biobank. The Journal of Clinical Endocrinology & Metabolism. 2020 Jul 4;105(10):e3606–19.
Vanegas-Cedillo PE, Bello-Chavolla OY, Ramírez-Pedraza N, Rodríguez Encinas B, Pérez Carrión CI, Jasso-Ávila MI, et al. Serum Vitamin D Levels Are Associated With Increased COVID-19 Severity and Mortality Independent of Whole-Body and Visceral Adiposity. Frontiers in Nutrition [Internet]. 2022 Jan 26 [cited 2022 Feb 15];9:813485. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8825804/
Campi I, Gennari L, Merlotti D, Mingiano C, Frosali A, Giovanelli L, et al. Vitamin D and COVID-19 severity and related mortality: a prospective study in Italy. BMC Infectious Diseases. 2021 Jun 14;21(1).
Dror AA, Morozov N, Daoud A, Namir Y, Yakir O, Shachar Y, et al. Pre-infection 25-hydroxyvitamin D3 levels and association with severity of COVID-19 illness. Jin D-Y, editor. PLOS ONE. 2022 Feb 3;17(2):e0263069.
General Health [Internet]. GrassrootsHealth. [cited 2022 Mar 13]. Available from: https://www.grassrootshealth.net/project/general-health/
What is the prevalence of vitamin D deficiency in the US? [Internet]. www.medscape.com. [cited 2022 Mar 13]. Available from: https://www.medscape.com/answers/128762-54281/what-is-the-prevalence-of-vitamin-d-deficiency-in-the-us
Wacker M, Holick MF. Sunlight and Vitamin D. Dermato-Endocrinology. 2013 Jan;5(1):51–108.
Shieh A, Chun RF, Ma C, Witzel S, Meyer B, Rafison B, et al. Effects of High-Dose Vitamin D2 Versus D3 on Total and Free 25-Hydroxyvitamin D and Markers of Calcium Balance. The Journal of Clinical Endocrinology & Metabolism [Internet]. 2016 Aug;101(8):3070–8. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4971338/
Carter GD, Berry J, Cavalier E, Durazo-Arvizu R, Gunter E, Jones G, et al. Biotin supplementation causes erroneous elevations of results in some commercial serum 25-hydroxyvitamin d (25OHD) assays. The Journal of Steroid Biochemistry and Molecular Biology [Internet]. 2020 Jun 1 [cited 2022 Mar 13];200:105639. Available from: https://pubmed.ncbi.nlm.nih.gov/32084550/
Supplemental Biotin May Interfere with Some Lab Tests [Internet]. GrassrootsHealth. [cited 2022 Mar 13]. Available from: https://www.grassrootshealth.net/blog/supplemental-biotin-may-interfere-lab-tests/#:~:text=When%20testing%20vitamin%20D%20levels
Oregon State University. Vitamin D [Internet]. Linus Pauling Institute. 2014. Available from: https://lpi.oregonstate.edu/mic/vitamins/vitamin-D
Knapen MHJ, Drummen NE, Smit E, Vermeer C, Theuwissen E. Three-year low-dose menaquinone-7 supplementation helps decrease bone loss in healthy postmenopausal women. Osteoporosis International. 2013 Mar 23;24(9):2499–507.
Mahdavi-Roshan M. Copper, magnesium, zinc and calcium status in osteopenic and osteoporotic post-menopausal women. Clinical Cases in Mineral and Bone Metabolism. 2015;
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