My recent report, Low Vitamin D Can Increase Risk for and Severity of COVID-19.  neglected to include a caution about taking excessive amounts of vitamin D in pills or by injection. You cannot be poisoned by vitamin D through sun exposure or diet alone, but vitamin D poisoning can occur when people take high-dose supplements for an extended time. Excess vitamin D can cause blood calcium levels to rise and after several months of having high blood calcium levels and having no symptoms at all, you can develop kidney failure and not even know it. You may develop nausea, vomiting, diarrhea, constipation or muscle weakness. You can also develop high blood pressure, kidney stones, or calcium in your arteries to increase risk for a heart attack. Since vitamin D accumulates in and is released very slowly from fat, it can take months for blood levels of vitamin D to return to normal and your symptoms to improve.

No Benefit From Extra Vitamin D
Several recent studies show that those who have normal blood levels of vitamin D (>20 ng/mL) gain no benefit from taking extra vitamin D by pills or injections.
• Healthy 55 to 70-year-old women who were not deficient in vitamin D gained no protection from osteoporosis, falls or broken bones after taking any dose of vitamin D for two years (JAMA, 2019;322(8):736-745).
• Those who took high doses of vitamin D (4000 and 10,000 IU/day) for three years lost far more bone than those who took the recommended 400 IU/day (J Bone and Mineral Research, September 11, 2020).
• People who take vitamin D pills do not have reduced rates of heart attacks, strokes, or cancer (N Engl J Med, 2019; 380:33-44).

Large Doses of Vitamin D Can Cause Bone Loss
Vitamin D is harmless in your body when it is bound to vitamin D receptors and carrier proteins. (J Clin Endocrinol Metab, 1986 Oct;63(4):954-9). However, having extra vitamin D floating in your system overwhelms vitamin D receptors to cause a marked increase in calcium to be absorbed from your gut (Am J Clin Nutr, 2004 Dec;80(6 Suppl):1689S-96S) and removed from your bones to cause high blood calcium levels (Oman Med J, 2011 May;26(3):201-4) that can bind to and damage every cell in your body. Excess vitamin D causes high blood calcium that can cause bone loss, brittle bones and bone pain. Vitamin K2 helps to keep calcium in bones. High levels of vitamin D also cause low levels of vitamin K2, with resultant loss of bone (Med Hypotheses, 2007;68(5):1026-34), and also cause loss of vitamin A.

Diagnosing Vitamin D Deficiency or Excess
The only way that you can find out if you are vitamin D deficient is to get a blood test for hydroxy vitamin D. There is conflict about the lowest level of normal. Most studies show that above 20 ng/mL is normal, while others show that it should be higher than 30 ng/mL to be normal. However, levels higher than 60ng/mL can harm you and you should never have blood levels above 150 ng/mL because that would put you at high risk for serious tissue damage.

My Recommendations
Vitamin D deficiency is common, particularly in the winter or in people with dark skin, but excessive vitamin D is harmful. I recommend getting a blood test for hydroxy vitamin D. If your blood levels of hydroxy vitamin D are below 20 ng/mL, take vitamin D3 pills of at least 1000 IU/day for one to two months. If your blood levels of vitamin D do not return to normal (>20 ng/mL), check with your doctor about taking higher doses or getting a medical evaluation for the cause of your deficiency. If your doctor recommends higher doses, you should be concerned about possible toxicity and should check blood levels of hydroxy vitamin D and calcium every month.
Sunlight: More than Vitamin D
Low Vitamin D Can Increase Risk for and Severity of COVID-19