Pearl of the Month

Vitamin D pearls


Case: A 56-year-old man with a history of type 2 diabetes, hypertension, hyperlipidemia, and obesity calls clinic to discuss concerns about COVID-19, stating: “I want to do everything I can to reduce my risk of infection.” In addition to physical distancing, mask wearing, hand hygiene, and control of chronic conditions, which of the following supplements would you recommend for this patient?

1. Coenzyme Q10 160 mg twice a day

2. Vitamin D 2,000 IU daily

3. Vitamin E 400 IU daily

4. Vitamin B12 1,000 mcg daily

Of these choices, vitamin D supplementation is likely the best option, based on the limited data that is available.

Vitamin D has been implicated in the prevention of many disease processes, including acute respiratory infections. Risk factors for worse COVID-19 outcome, such as older age, obesity, and more pigmented skin are also risk factors for vitamin D deficiency. This makes the study of vitamin D and COVID-19 both challenging and relevant.

In a recent study of 7,807 people living in Israel, Merzon and colleagues found that low plasma vitamin D level was an independent risk factor for COVID-19 infection. Mean plasma vitamin D level was significantly lower among those who tested positive for COVID-19 (19.00 ng/mL) than negative (20.55 ng/ mL). After controlling for demographic variables and several medical conditions, the adjusted odds ratio of COVID-19 infection in those with lower vitamin D was 1.45 (95% confidence interval, 1.08-1.95; P < .001). However, the odds of hospitalization for COVID-19 was not significantly associated with vitamin D level.1

Vitamin D written on a blackboard surrounded by vitamin D dense foods. yulka3ice/Getty Images

Prior studies have also looked at vitamin D and respiratory infection. Martineau and colleagues analyzed 25 randomized, controlled trials with a pooled number of 11,321 individuals, including healthy ones and those with comorbidities, and found that oral vitamin D supplementation in daily or weekly doses had a protective effect against acute respiratory infection (adjusted odds ratio, 0.88; 95% CI, 0.81-0.96; P < .001). Patients with vitamin D deficiency (less than 25 nmol/L) experienced the most protective benefit. Vitamin D did not influence respiratory infection outcome.2

These studies suggest an adequate vitamin D level may be protective against infection with COVID-19, but who will benefit from vitamin D supplementation, and in what dose? Per U.S. Preventive Services Task Force guidelines, there is insufficient evidence to recommend screening for vitamin D deficiency in asymptomatic adults. Regarding daily dietary intake, the Institute of Medicine recommends 600 IU for persons aged 1-70, and 800 IU for those aged over 70 years. Salmon (447 IU per 3 oz serving), tuna (154 IU), and fortified milk (116 IU) are among the most vitamin D–rich foods.3 The recommended upper level of intake is 4,000 IU/day.

Too much of a good thing?

Extra vitamin D is stored in adipose tissue. If it builds up over time, storage sites may be overwhelmed, causing a rise in serum D level. While one might expect a subsequent rise in calcium levels, studies have shown this happens inconsistently, and at very high vitamin D levels, over 120 ng/mL.4 Most people would have to take at least 50,000 IU daily for several months to see an effect. The main adverse outcome of vitamin D toxicity is kidney stones, mediated by increased calcium in the blood and urine.

Ms. Jody Sharninghausen

Jody Sharninghausen

Several animal models have demonstrated hypervitaminosis D–induced aortic and coronary artery calcification. Like with kidney stones, the mechanism appears to be through increased calcium and phosphate levels. Shroff and colleagues studied serum vitamin D levels and vascular disease in children with renal disease on dialysis and found a U-shaped distribution: Children with both low and high vitamin D levels had significantly increased carotid artery intima-media thickness and calcification.5 Given the specialized nature of this population, it’s unclear whether these results can be generalized to most people. More studies are warranted on this topic.

Other benefits

Vitamin D is perhaps most famous for helping to build strong bones. Avenell and colleagues performed a Cochrane meta-analysis of vitamin D supplementation in older adults and found that vitamin D alone did not significantly reduce the risk of hip or other new fracture. Vitamin D plus calcium supplementation did reduce the risk of hip fracture (nine trials, pooled number of individuals was 49,853; relative risk, 0.84; P = .01).6

Dr. Douglas S. Paauw, University of Washington, Seattle

Dr. Douglas S. Paauw

A lesser-known benefit of vitamin D is muscle protection. A prospective study out of the Jewish Hospital of Cincinnati followed 146 adults who were intolerant to two or more statins because of muscle side effects and found to have a vitamin D level below 32 ng per mL. Subjects were given vitamin D replacement (50,000 units weekly) and followed for 2 years. On statin rechallenge, 88-95% tolerated a statin with vitamin D levels 53-55 ng/mL.7


Vitamin D supplementation may protect against COVID-19 infection and has very low chance of harm at daily doses at or below 4,000 IU. Other benefits of taking vitamin D include bone protection and reduction in statin-induced myopathy. The main adverse effect is kidney stones.

Ms. Sharninghausen is a medical student at the University of Washington, Seattle. Dr. Paauw is professor of medicine in the division of general internal medicine at the University of Washington and serves as third-year medical student clerkship director at the University of Washington. He is a member of the editorial advisory board of Internal Medicine News. Dr. Paauw has no conflicts to disclose. Contact him at [email protected].


1. Merzon E et al. Low plasma 25(OH) vitamin D level is associated with increased risk of COVID‐19 infection: An Israeli population‐based study. FEBS J. 2020. doi: 10.1111/febs.15495.

2. Martineau AR et al. Vitamin D supplementation to prevent acute respiratory tract infections: Systematic review and meta-analysis of individual participant data. BMJ. 2017;356:i6583. doi:10.1136/bmj.i6583

3. “How to Get More Vitamin D From Your Food,” Cleveland Clinic. 2019 Oct 23.

4. Galior K et al. Development of vitamin d toxicity from overcorrection of vitamin D Deficiency: A review of case reports. Nutrients. 2018;10(8):953. doi: 10.3390/nu10080953

5. Shroff R et al. A bimodal association of vitamin D levels and vascular disease in children on dialysis. J Am Soc Nephrol. 2008;19(6):1239-46. doi: 10.1681/ASN.2007090993.

6. Avenell A et al. Vitamin D and vitamin D analogues for preventing fractures in post‐menopausal women and older men. Cochrane Database Syst Rev. 2014 Apr 14;2014(4):CD000227. doi: 10.1002/14651858.CD000227.pub4.

7. Khayznikov M et al. Statin intolerance because of myalgia, myositis, myopathy, or myonecrosis can in most cases be safely resolved by vitamin D supplementation. N Am J Med Sci. 2015;7(3):86-93. doi:10.4103/1947-2714.153919

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