Update: Using the data from the first 10 days of August, I’m predicting 1,759,899 cases and 30,798 deaths in the U.S. in the whole of August. Method: totals from first 10 days times 3.2258 equals the case and death totals.
Dear online friends, supporters, and readers, I feel I have a moral obligation to inform you of something that is important to our health. However, it is a medical matter, not yet proven beyond doubt, and you should know that I am not a doctor or healthcare professional.
Since February, I have been researching and writing about Covid-19, first here (ronconte.com) and later at my Covid blog (covid.us.org). And it has reached the point now that certain conclusions have become clear to me.
Vitamin D and Covid-19
18 studies support the theory that having high blood levels of vitamin D reduces Covid-19 risks, including risk of infection [7, 8, 9, 11, 12, 14, 16], of having a severe case [1, 3, 4, 5, 15, 17], of needing hospitalization, ICU care, and/or mechanical ventilation [2, 10, 14, 15], as well as the risk of dying from Covid-19 [4, 6, 7, 9, 12, 13, 17, 18]. See endnotes [1-18].
In one study , over 90% of patients with normal levels of vitamin D (92.7%) had mild cases of Covid-19; only 3.6% had a moderate (or “ordinary”) case, and another 3.6% had a severe or critical case. But among the patients with vitamin D deficiency, 79.2% had a severe or critical case and only 7.8% had a mild case .
The other studies each support one or more of the risk reductions listed above. The combination of all those studies is quite convincing to me. However, health authorities like the FDA do not permit anyone to assert that increasing one’s blood level of vitamin D, by supplementation or sunshine, will have the above suggested beneficial risk reductions regarding Covid-19. This is because the studies are not considered definitive at this point in time. So all I can tell you is that these studies exist, and they propose, as a theory, what I’ve summarized above. You can read each study for yourself, as links are included in the Endnotes. Perhaps these studies are wrong. Decide for yourself. I am not making any definitive medical claims, but merely explaining what the preliminary research says so far. And, as I said, I feel I have a moral obligation to make this information known.
In addition, research in recent decades has shown that having optimum blood levels of vitamin D may possibly reduce risk of: stroke , multiple sclerosis , rheumatoid arthritis , type 2 diabetes , breast cancer , prostate cancer , colon cancer , and all-cause mortality . One study found that blood levels of vitamin D of 52 ng/ml or higher (130 nmol/L) reduce risk of breast cancer by 50% . Yet vitamin D deficiency is very common throughout the United States and the world.
I am not a physician. I suggest that you might possibly want to talk to your doctor about vitamin D. But I am not giving medical advice, but merely information.
If you decide to take vitamin D, how much should you take?
(The term “25(OH)D” refers to the type of vitamin D that circulates in the bloodstream.)
Grant, William B., et al., in the article “Evidence that vitamin D supplementation could reduce risk of influenza and COVID-19 infections and deaths,” in the journal Nutrients, state the following:
“To reduce the risk of infection, it is recommended that people at risk of influenza and/or COVID-19 consider taking 10,000 IU/d of vitamin D3 for a few weeks to rapidly raise 25(OH)D concentrations, followed by 5000 IU/d. The goal should be to raise 25(OH)D concentrations above 40–60 ng/mL (100–150 nmol/L). For treatment of people who become infected with COVID-19, higher vitamin D3 doses might be useful.” 
Charoenngam and Holick, “Immunologic Effects of Vitamin D on Human Health and Disease.” Nutrients: “It is therefore proposed that supplementation of vitamin D can reduce the risk and severity of COVID-19 infection.”  Both the Grant and the Charoenngam/Holick studies were peer-reviewed.
When Dr. William Grant  was challenged on his recommendation to take 10,000 IU/day of vitamin D for a few weeks, followed by 5,000 IU/day, he responded:
“We strongly disagree that vitamin D supplementation should be held in abeyance for prevention until such RCTs are completed and reported. Those at highest risk of infection due to having chronic disease, low 25(OH)D status, and/or being in frequent contact with others likely to be infected should be taking vitamin D,” he says.
“As noted, there is mounting evidence that vitamin D can reduce risk and severity of RTIs including that the mechanisms are known, that there are many health benefits of higher 25(OH)D concentrations, and that there are very few adverse effects of vitamin D3 supplementation… Thus, there is much to gain and little to lose by taking vitamin D supplements now for COVID-19 prevention.” 
Please understand that some other physicians and researchers disagree, saying that the current evidence for vitamin D’s benefits against Covid-19 is not strong and that taking very high doses of vitamin D is not without risk as this article explains. However, all agree that a vitamin D deficiency should be corrected to within a normal range (30 to 100 ng/ml, which is 75 to 250 nmol/L).
This Winter Could Be Bad
The second part to my moral obligation also concerns vitamin D. The levels of vitamin D in the blood, in the general population, rise in the summer and fall in the winter. This has the consequence of making some diseases “seasonal”, typically meaning that the winter season sees many more cases of the disease than the summer. As discussed above, higher vitamin D levels may be protective against Covid-19 as well as other diseases. This theoretically may cause a higher number of cases, and a greater average severity for those who become ill in winter, raising both the case rate and the case fatality rate.
Is Covid-19 seasonal? Experts do not agree. However, some studies have proposed that it might be. One study concluded that the data from Covid-19 and weather patterns is “consistent with the behavior of a seasonal respiratory virus. ” Another study found that the similar SARS virus is seasonal . And three studies found that the human coronaviruses that cause colds are seasonal [33, 34, 35]. One study stated, about these cold-type viruses: “Coronaviruses are sharply seasonal.” 
If Covid-19 is seasonal, then in winter, due to lower vitamin D levels, the number of cases and the death rate will increase. The degree of increase is very uncertain. The number of cases at the winter peak, which could be anywhere from Dec. to Mar., could be a multiple of the number of cases in July or August or September, the seasonal lows.
If the number of cases per month is higher, the number of deaths will be higher. But it may also be the case that the case fatality rate will be higher, i.e. as a percentage. So if cases double and the rate also doubles, the number dead will quadruple. How bad could this be? July saw 2 million cases in the U.S. with 26,653 deaths. The winter peak months could see hundreds of thousands of deaths per month.
There is a Second Wave of Covid-19 cases and deaths coming this winter. It can be avoided with a massive vitamin D “supplementation and sunshine” program. Without a vaccine and without a vitamin D program, the hospital and overall healthcare system could break.
The experts do not agree that there will be a second wave this winter. They are predicting either a reduction in cases, or a slow rise. But we know that vitamin D levels are lower, population wide, in winter. So the degree to which vitamin D affects Covid-19 will determine the degree of severity of the winter wave.
September will be the yearly low for cases and death rate. And, as I understand the situation, the lower the low, the higher the high. If Sept. is particularly low, it means vitamin D has a bigger positive effect, which means vitamin D deficiency has a bigger negative effect. If September cases rises, then the winter might not be so bad.
This is just a suggestion, from your online friend (or acquaintance). Maybe you would like to follow my example, and take a vitamin D pill each day. Getting outdoors with sunshine on skin will also help. But the only sure way to raise vitamin D levels is with supplementation.
1. Alipio, Mark. “Vitamin D Supplementation Could Possibly Improve Clinical Outcomes of Patients Infected with Coronavirus-2019 (COVID-19).” SSRN 3571484 (9 April 2020).
2. Lau, Frank H., et al. “Vitamin D insufficiency is prevalent in severe COVID-19.” medRxiv (28 April 2020).
3. Daneshkhah, Ali, et al. “The Possible Role of Vitamin D in Suppressing Cytokine Storm and Associated Mortality in COVID-19 Patients.” medRxiv (2020).
4. Davies, Gareth, Attila R. Garami, and Joanna C. Byers. “Evidence Supports a Causal Model for Vitamin D in COVID-19 Outcomes.” medRxiv (2020).
5. De Smet, Dieter, et al. “Vitamin D deficiency as risk factor for severe COVID-19: a convergence of two pandemics.” medRxiv (2020).
6. Raharusun, Prabowo, et al. “Patterns of COVID-19 Mortality and Vitamin D: An Indonesian Study.” (2020).
7. Ilie, Petre Cristian, Simina Stefanescu, and Lee Smith. “The role of vitamin D in the prevention of coronavirus disease 2019 infection and mortality.” Aging Clinical and Experimental Research (2020): 1.
8. D’Avolio, Antonio, et al. “25-hydroxyvitamin D concentrations are lower in patients with positive PCR for SARS-CoV-2.” Nutrients 12.5 (2020): 1359.
9. Laird, E., et al. “Vitamin D and Inflammation: Potential Implications for Severity of Covid-19.” Ir Med J; Vol 113; No. 5; P81: 2020.
10. Faul, J.L., et al. “Vitamin D Deficiency and ARDS after SARS-CoV-2 Infection.” Ir Med J; Vol 113; No. 5; P84: 2020.
11. Meltzer, David O., et al. “Association of Vitamin D Deficiency and Treatment with COVID-19 Incidence.” medRxiv (2020).
12. Li, Yajia, et al. “Sunlight and vitamin D in the prevention of coronavirus disease (COVID-19) infection and mortality in the United States.” (2020).
13. Pugach, Isaac Z. and Pugach, Sofya “Strong Correlation Between Prevalence of Severe Vitamin D Deficiency and Population Mortality Rate from COVID-19 in Europe.” medRxiv (2020).
14. Merzon, Eugene, et al. “Low plasma 25(OH) vitamin D3 level is associated with increased risk of COVID-19 infection: an Israeli population-based study.” medRxiv (2020). — Low vitamin D increased risk (adjusted OR) of infection with Covid-19 by 45% and of hospitalization for Covid by 95%.
15. Panagiotou, Grigorios et al., “Low serum 25-hydroxyvitamin D (25[OH]D) levels in patients hospitalised with COVID-19 are associated with greater disease severity: results of a local audit of practice.” medRxiv (2020). Conclusion: “we found that patients requiring ITU admission [in the ICU] were more frequently vitamin D deficient than those managed on medical wards [on the floor], despite being significantly younger.”
PDF file Link
16. Chang, Timothy S., et al. “Prior diagnoses and medications as risk factors for COVID-19 in a Los Angeles Health System.” medRxiv (2020).
~ Risk factors included vitamin D deficiency, which increased risk of COVID-19 diagnosis by 80% (OR 1.8 [1.4-2.2], p=5.7 x 10-6).
17. Maghbooli, Zhila, et al. “Vitamin D Sufficiency Reduced Risk for Morbidity and Mortality in COVID-19 Patients.” Available at SSRN 3616008 (2020).
~ Vitamin D sufficiency reduced clinical severity and inpatient mortality.
18. Panarese and Shahini, “Letter: Covid-19 and Vitamin D” Alimentary Pharmacology and Therapeutics, April 12, 2020.
Link to Letter
~ Covid-19 mortality increases with increasing latitude (by nation), and vitamin D blood levels decrease with increasing latitude. The authors propose that low levels of vitamin D increase Covid-19 mortality.
19. Marniemi et al., Dietary and serum vitamins and minerals as predictors of myocardial infarction and stroke in elderly subjects; Nutrition, Metabolism & Cardiovascular Diseases. Volume 15, Issue 3 , Pages 188-197, June 2005. Study Link
20. Munger et al., Vitamin D intake and incidence of multiple sclerosis; Neurology. January 13, 2004 vol. 62 no. 1, p. 60-65. Study Link
21. Merlino et al., Vitamin D intake is inversely associated with rheumatoid arthritis: Results from the Iowa Women’s Health Study; Arthritis & Rheumatism. Volume 50, Issue 1, pages 72-77, January 2004. Study Link
22. Pittas et al., Vitamin D and Calcium Intake in Relation to Type 2 Diabetes in Women; Diabetes Care. March 2006 vol. 29 no. 3 650-656. Study Link
23. Garland et al., Vitamin D and prevention of breast cancer: Pooled analysis; The Journal of Steroid Biochemistry and Molecular Biology, Volume 103, Issues 3-5, March 2007, Pages 708-711; Study Link
24. Garland et al., The Role of Vitamin D in Cancer Prevention; American Journal of Public Health. 2006 February; 96(2): 252-261. Study Link
25. Gorham et al., Optimal Vitamin D Status for Colorectal Cancer Prevention: A Quantitative Meta-Analysis; American Journal of Preventive Medicine. Volume 32, Issue 3 , Pages 210-216, March 2007; Study Link
26. Garland et al., The Role of Vitamin D in Cancer Prevention; American Journal of Public Health. 2006 February; 96(2): 252-261. Study Link
27. Garland et al., Vitamin D and prevention of breast cancer: Pooled analysis; The Journal of Steroid Biochemistry and Molecular Biology, Volume 103, Issues 3-5, March 2007, Pages 708-711; Study Link
28. Grant, William B., et al. “Evidence that vitamin D supplementation could reduce risk of influenza and COVID-19 infections and deaths.” Nutrients 12.4 (2020): 988. Study Link
29. Charoenngam and Holick, “Immunologic Effects of Vitamin D on Human Health and Disease.” Nutrients 2020, 12(7), 2097; Study Link
30. William Grant, interview published at nutraingredients.com; 22-May-2020 By Nikki Hancocks. Article Link
31. Sajadi, Mohammad M., et al. “Temperature, Humidity, and Latitude Analysis to Estimate Potential Spread and Seasonality of Coronavirus Disease 2019 (COVID-19).” JAMA Network Open 3.6 (2020): e2011834-e2011834. Study Link
32. Yuan, Jingsong, et al. “A climatologic investigation of the SARS-CoV outbreak in Beijing, China.” American journal of infection control 34.4 (2006): 234-236.
33. Edridge, Arthur WD, et al. “Coronavirus protective immunity is short-lasting.” MedRxiv (2020). PDF file of Study
34. Komabayashi, Kenichi, et al. “Seasonality of human coronavirus OC43, NL63, HKU1, and 229E infection in Yamagata, Japan, 2010–2019.” Japanese Journal of Infectious Diseases (2020): JJID-2020.
35. Monto, Arnold S., et al. “Coronavirus occurrence and transmission over 8 years in the HIVE cohort of households in Michigan.” The Journal of infectious diseases (2020). Study Link