Vitamin D
Best studied for: Bone health; Immune support; Low mood and seasonal depression. Supports bone strength, immune defense, mood, muscle function.
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What is v itamin D ? Vitamin D is a fat-soluble vitamin that helps the body absorb calcium and maintain bone health. It can be obtained from food sources or synthesized by the body through exposure to sunlight. How does it work? Vitamin D works by regulating the levels of calcium and phosphorus in the body, which are essential for bone health. It also plays a role in immune function, muscle function, and reducing inflammation. What are the active ingredients that are important for its medicinal properties? The active form of vitamin D is called calcitriol, which is produced by the body from vitamin D. What forms does it come in? Vitamin D is available in supplements, as well as in foods such as fatty fish, fortified dairy products, and egg yolks. What if there’s an imbalance or deficiency? A deficiency in vitamin D can cause bone and muscle weakness, and increase the risk of fractures and falls. It has also been associated with an increased risk of certain cancers, autoimmune disorders, and respiratory infections. When was it first used for medicinal purposes? Vitamin D was first used to treat rickets, a bone disease caused by vitamin D deficiency, in the early 20th century.
Helps
What does Vitamin D help with? Vitamin D is a nutrient your skin makes from sunlight. You also get small amounts from food, and from pills or drops. Many people run low in winter, or if they spend their days indoors. The evidence is strong in some places and thin in others. Trials back it best for bone health and for raising low blood levels. For mood, sleep, blood pressure and hormones, the findings are mixed. Low vitamin D levels shown on a blood test Strong evidence — many randomised trials showing oral vitamin D raises blood levels. A low level means a blood reading under 20 ng/mL. Trials show that taking vitamin D by mouth raises that reading. Low readings are common in older adults, people with darker skin, people who are overweight, and those who live far north. Evidence grade A · Traditional tier T0 Thinning bones and broken bones as you age Strong evidence — consistent randomised trials in older adults, mostly vitamin D given with calcium. Vitamin D is well established to help the body take up calcium from food. Without it, the body draws calcium out of bone. In trials, older adults who took vitamin D with calcium held more bone density and broke fewer bones. Evidence grade A · Traditional tier T0 Catching every cold and chest infection Good evidence — randomised winter trials of vitamin D, plus lab work on immune cells. In lab work, vitamin D switched on immune cells that hunt germs, called T-cells and macrophages. People with low blood levels report getting sick more often. In winter trials, those who took vitamin D had fewer airway infections. Evidence grade B · Traditional tier T0 Aching muscles, weakness and being worn out Early evidence — small human studies in people who were already low. Doctors list low vitamin D as an often missed cause of muscle aches and tiredness. In studies of people who were low, raising the level improved strength and eased widespread pain. Its role in muscle fibres and in cell energy comes from lab science, not from trials of these symptoms. Evidence grade C · Traditional tier T0 Winter blues and low mood Early evidence — mixed human studies, strongest in people who were low. Low vitamin D is linked, again and again, with higher rates of depression. In studies, people who were low reported better mood after taking it. Vitamin D receptors sit in mood areas of the brain, but that is lab work only. Evidence grade C · Traditional tier T0 Poor sleep Early evidence — small clinical studies, mainly in people who were low. Short, broken sleep is linked with low vitamin D levels. In clinical studies, people who were low slept longer and better once their levels came up. Receptors in sleep areas of the brain are a lab finding, not proof of a sleep effect. Evidence grade C · Traditional tier T0 High blood pressure Evidence doesn't support this — mostly link studies in groups of people; trial results conflict. Many studies link low vitamin D with higher blood pressure and higher heart risk. Those are links, not proof that pills bring pressure down. Lab work shows vitamin D acting on the renin-angiotensin system, which helps set blood pressure. Evidence grade D · Traditional tier T0 Low testosterone in men Evidence doesn't support this — small studies in men who were low; results modest and not consistent. Research links a man's vitamin D level with his testosterone level. In some studies, men who were low and took it steadily saw small rises over time. The size of the change is modest and not the same across studies. Receptors in the testes were found in lab work. Evidence grade D · Traditional tier T0 Autoimmune conditions such as MS, rheumatoid arthritis and type 1 diabetes Evidence doesn't support this — link studies in groups of people plus early, emerging trials. Low vitamin D goes along with higher rates of these conditions. That is a pattern seen in groups, not proof of cause. Work on how vitamin D calms the immune system is early, and trials have not shown that pills change the course of
