Nearly four months into sheltering-in-place and the risk of COVID-19 remains of high concern. I mentioned vitamin D in my February email and I find that it continues to be discussed and now researched as to how it may influence COVID-19. I thought it would be prudent to share more on this topic.
Vitamin D and COVID-19
Known for its anti-inflammatory, immunomodulatory, bone protective, and anti-cancer effects, vitamin D has far-reaching therapeutic effects. And there’s a possibility that vitamin D may help lower the risk of COVID-19 and/or the severity of the virus. While, undoubtedly, more research is needed, there are some studies suggesting that there may be a link between vitamin D and COVID-19. Research seems to be quickly evolving on this topic. Adequate vitamin D levels may offer those with COVID-19 a survival advantage by helping them avoid a cytokine storm, where the immune system overreacts and attacks your body’s own cells and tissues.
One study has reported lower vitamin D levels in patients who tested positive for SARS-CoV-2. Similarly, a different study observed negative correlations between vitamin D levels and the number of patients testing positive for COVID-19. Vitamin D levels are especially low in the aging population, a group at high risk for COVID-19. This European study reported severely low levels of vitamin D in the older populations, particularly in Spain, Italy, and Switzerland. Another theory has been related to the timing of COVID-19 in which the outbreak occurred during the winter when vitamin D levels are at their lowest. Additionally, vitamin D deficiency has been found to contribute to acute respiratory distress syndrome. Vitamin D supplementation appears to lower the prevalence of acute respiratory infections.
Vitamin D and Cancer
Observations revealing lower rates of certain cancers in regions with greater yearly sun exposure led to research exploring biologic associations between vitamin D and cancer. Discoveries that the vitamin D receptor is found in most cells including many cancer cells and that vitamin D helps regulate genes that modulate cell proliferation, differentiation and apoptosis support a biologic role in carcinogenesis. Furthermore, vitamin D controls immune cell regulation and differentiation, gut barrier function and antimicrobial peptide synthesis, all of which may serve as protective factors against cancer. While more research is necessary, vitamin D levels have been associated with a lower risk of cancer and possibly improved cancer survival, particularly for colorectal cancer. Vitamin D sufficiency is important for overall health including cancer prevention.
Vitamin D Sources and Testing
With few natural food sources of vitamin D and cultural emphasis on safe sun exposure, fortified foods and dietary supplements have become increasingly important for maintaining vitamin D sufficiency and/or correcting a deficiency. We generate the majority of our vitamin D through skin synthesis of sunlight via ultraviolet B. While the melanin pigment absorbs ultraviolet radiation and is protective against skin damage, it also reduces vitamin D synthesis in the skin. Hence, those with darker pigmented skin types are at greater risk of vitamin D deficiency. Dietary sources include cold-water fish, eggs, mushrooms exposed to ultraviolet light, and fortified products, such as milk, soy milk, and cereals.
Vitamin D2 (ergocalciferol) from plant sources and Vitamin D3 (cholecalciferol) from animal sources (and synthesized in the skin) are available as dietary supplements. Each form can respectively raise serum 25-hydroxyvitamin D2 and 25-hydroxyitamin D3 [25(OH)D] levels by 10 ng/mL per 1000 IU taken. The bioavailability of vitamin D3 is significantly greater than vitamin D2.
Recent meta-analyses indicate that vitamin D3 is more efficacious at raising serum 25(OH)D concentrations than is vitamin D2 though several prospective studies have found them to be equally effective in raising and maintaining serum 25(OH)D levels in children and adults. Disagreement over optimal and safe 25(OH)D levels for overall health and cancer prevention remains widespread. Complicating the determination of ideal 25(OH)D levels is the observation that vitamin D is sequestered in fat and therefore may not be as readily available in overweight and obese persons as in persons of healthy weight. The Endocrine Society suggests that maintenance of a 25(OH)D level of 40 to 60 ng/mL is ideal (this takes into account assay variability); research suggests that up to 100 ng/mL is safe. Due to the likelihood of a biochemical deficiency without clinical symptoms or signs of deficiency, a serum 25(OH)D level is recommended. More appropriate dosing of vitamin D supplementation can be made once a serum 25(OH)D level has been established.
Vitamin D Recommendation
Due to the myriad of therapeutic properties, it’s wise to ensure adequate vitamin D levels. As a fat-soluble vitamin, vitamin D will be best absorbed when consumed with a fat-containing meal. Additionally, vitamin K2 helps enhance the absorption of vitamin D, so opting for a product that contains both D3 and K2 is preferred. Most individuals will need 2000-5000IU D3 daily to achieve sufficient 25(OH)D serum levels. During the pandemic, it may be suggested to take a higher dosage. In time, we should learn more about the association of vitamin D and COVID-19 and perhaps be able to refine recommendations. At this time, the goal should be to raise or maintain 25(OH)D concentrations above 40-60 ng/mL.