Less than six percent of North Americans suffer from vitamin D deficiency, but nearly 20 percent 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, 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).
Current Guidelines 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).
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)
My Recommendations You probably do not need to take vitamin D pills if your blood level of hydroxy vitamin D is above 20 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 20 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 (<20 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.
See Sunlight: More than Vitamin D
Recent ArticlesElectric-Assist Bikes and Trikes
June 14th, 2019
High Plant Diet Wins Again
June 14th, 2019
Tim Conway and Normal Pressure Hydrocephalus
June 10th, 2019
Reduce Inflammation and Clotting to Prevent Heart Attacks
June 9th, 2019
Short Intervals are Best
June 9th, 2019