Nearly 20 percent of North American adults take vitamin D pills. It is true that it is difficult to get adequate levels of vitamin D from sunshine during the winter months, but vitamin D is not a miracle vitamin that treats and prevents all sorts of diseases. A recent study of 5,108 men and women showed that vitamin D pills did not help to prevent heart attacks (JAMA Cardiol, published online April 5, 2017), and another study showed that large doses of vitamin D did not help to prevent cancer (JAMA, Mar 28, 2017;317(12):1234-1243).
No Proven Benefit from High Doses of Vitamin D
The main function of vitamin D is to help keep bones strong and control calcium metabolism. Vitamin D increases calcium absorption in the intestines and strengthens bones by increasing bone remodeling and increasing the effects of parathyroid hormones. Almost all of the other reported functions of vitamin D are controversial.
There is no proven benefit from taking high doses of vitamin D (>1000 IU/day) or having very high blood levels (>20ng/ml). Raising blood levels of hydroxy vitamin D from 20 to 30 ng/ml with high doses of vitamin D pills increases calcium absorption by only one percent and does not increase bone mineral density or physical function, compared with placebo (Curr Opin Endocrinol Diabetes Obes, Dec 2016;23(6):440-444).
High doses of vitamin D can cause nausea, constipation, kidney stones, frequent urination, muscle weakness, irregular heartbeats and possibly arteriosclerosis. A study from Denmark showed that very high blood levels of hydroxy vitamin D above 140 ng/ml are associated with increased risk of premature death (J Clin Endocrinol Metab, Aug 2012;97(8):2644-52). High-dose vitamin D3 supplements (70,000 IU·wk for 12 weeks) caused a significant increase of a toxic vitamin D metabolite called 24,25[OH] vitamin D, reduced parathyroid levels and decreased body responses to vitamin D (Med Sci Sports Exerc, Feb, 2017;49(2):349-356).
Confusion about Vitamin D Deficiency
It is difficult for doctors to identify patients with vitamin D deficiency because most commercial laboratories do not offer a test for the active form of vitamin D, which is 1,25 dihydroxy vitamin D. Instead, laboratories measure an inactive form called hydroxy vitamin D. The massive doses of vitamin D recommended by some doctors do not raise the active form of vitamin D because your own body tries to protect you from poisoning by breaking down the active form. You cannot develop vitamin D poisoning from too much sunlight because sunlight breaks down vitamin D just as it helps your body to make it, so as you keep exposing your skin to sunlight, blood levels reach a certain level and do not rise higher. Massive doses of vitamin D pills such as 150,000 IU every three months fail to raise blood levels of the active 1,25 hydroxy vitamin D ((J Adolesc Health, Jul, 2015;57(1):19-23).
Many studies show that people with dark skin have lower levels of the inactive form of vitamin D. It’s a different story when doctors measure blood levels of the active form of vitamin D. People with dark skin are able to use a much higher proportion of the active form of vitamin D (N Engl J Med, Nov 21, 2013;369(21):1991-2000).
The Institute of Medicine recommends that adults need only 600–800 IU of vitamin D per day and that blood levels of hydroxy vitamin D do not need to be higher than 20 ng per milliliter (Curr Opin Endocrinol Diabetes Obes, Dec 2016;23(6):440-444). Higher blood levels of vitamin D (greater than 20 ng/ml) do not make bones stronger than lower blood levels as they do not reduce levels of parathyroid hormone or bone resorption (Curr Rheumatol Rep, June 2011;13(3):257-64). 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.
Large doses (4000 IU/day) of vitamin D did not slow declining physical function in sedentary men over 70 (Journal of the American Geriatrics Society, 11/22/2016). Furthermore, for most people, high dose vitamin D pills (greater than 2000 IU/day) are not going to improve health and may even harm you (N Engl J Med, Nov 10, 2016;375:1817-1820).
Proposed Uses of Vitamin D for Specific Conditions
Several recent studies recommend vitamin D supplementation for specific populations or symptoms:
• People with generalized muscle and joint pain and blood levels of hydroxy vitamin D below 20 ng/ml (International Journal of Rheumatic Diseases, 11/21/2016)
• Women with postmenopausal osteoporosis (Bone, 11/10/2016)
• People with muscle and joint pain from an auto immune disease called lupus who also have a positive anti-nuclear antibody titer and low blood levels of hydroxy vitamin D (Cancer Epidemiology, Biomarkers & Prevention, 11/17/2016)
• Elderly inactive people who do not go outdoors; 56 studies involving almost 100,000 people over 70 showed that taking 800 IU of vitamin D pills is associated with a slightly prolonged lifespan (Cochrane Database Syst Rev, Jan 2014;10;(1):CD007470)
• Hospitalized intensive-care, critically ill adult patients with hydroxy vitamin D levels below 20 ng/ml (Journal of Critical Care, 11/14/2016)
• People with muscle pain from taking statin drugs to lower cholesterol, who also have blood levels of hydroxy vitamin D below 20 ng/ml (Atherosclerosis, 11/22/2016)
• Diabetics with high blood cholesterol (LDL over 100) and low blood hydroxy vitamin D (<20 ng/ml) (Diabetology & Metabolic Syndrome, 11/22/2016)
• Possibly long-term care residents over 70; may help to prevent respiratory infections (Journal of the American Geriatrics Society, 11/22/2016)
You probably do not need to take vitamin D pills if your blood level of hydroxy vitamin D is above 30 ng/ml unless you have a condition that your doctor feels puts you at increased risk for the signs and symptoms of a deficiency. You can take up to 1000 IU/day of vitamin D pills if your blood levels are below 30 ng/ml. Most researchers and clinicians now feel that, with few exceptions, high doses of vitamin D are not beneficial and are potentially harmful. You should not take doses of vitamin D greater than 1000 IU/day unless your doctor diagnoses a specific reason to do so. People who could possibly benefit from treating low blood levels of hydroxy vitamin D (<30 ng/ml) include those who:
• are inactive and do not go outdoors
• suffer from generalized muscle and joint pain
• are athletes with recurrent injuries and decreased performance
• have weak bones (osteoporosis)
• are diabetic, particularly if LDL cholesterol is over 100
• have an auto-immune disease
• are critically ill or debilitated
• suffer from muscle pain from taking statin drugs.