Vitamin D is an essential vitamin that helps regulate calcium and phosphorus in the body. It also plays a role in maintaining proper bone structure.

There are different forms of vitamin D, including ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3). Vitamin D is found in fish, eggs, and fortified milk. It's also made in the skin when exposed to sunlight. During periods of sunlight, vitamin D is stored in fat and then released when sunlight is not available.

Vitamin D supplements are commonly used to treat and prevent vitamin D deficiency. People who don't get enough sun and people who are 65 years or older are at risk for deficiency. People also use vitamin D for weak and brittle bones, heart disease, asthma, hay fever, and many other conditions, but there's no good scientific evidence to support many of these uses. There is also no strong evidence to support using vitamin D supplements for COVID-19. But it is important to maintain healthy levels of vitamin D. This can be done by taking 400-1000 IU of vitamin D daily or spending 15-30 minutes in the sun each day.

USES

Effective for

• A rare, inherited bone disorder marked by low levels of phosphate in the blood (familial hypophosphatemia). Taking specific forms of vitamin D, called calcitriol or dihydrotachysterol, by mouth along with phosphate supplements is effective for treating bone disorders in people with low levels of phosphate in the blood.
• Underactive parathyroid (hypoparathyroidism). Taking specific forms of vitamin D, called dihydrotachysterol, calcitriol, or ergocalciferol, by mouth is effective for increasing calcium blood levels in people with low parathyroid hormone levels.
• Softening of the bones (osteomalacia). Taking vitamin D3 by mouth is effective for treating this condition.
• A bone disorder that occurs in people with kidney disease (renal osteodystrophy). Taking a specific form of vitamin D, called calcitriol, by mouth helps to manage low calcium levels and prevent bone loss in people with kidney failure.
• Rickets. Taking vitamin D by mouth is effective for preventing and treating rickets. A specific form of vitamin D, called calcitriol, should be used in people with kidney failure.
• Vitamin D deficiency. Taking vitamin D by mouth is effective for preventing and treating vitamin D deficiency.

Likely Effective for

• Bone loss in people taking drugs called corticosteroids. Taking vitamin D by mouth prevents bone loss in people taking drugs called corticosteroids. Also, taking vitamin D alone or with calcium seems to improve bone density in people with existing bone loss caused by using corticosteroids.
• Weak and brittle bones (osteoporosis). Taking vitamin D3 by mouth along with calcium seems to help prevent bone loss and bone breaks in people with osteoporosis.
• Psoriasis. Applying vitamin D in the form of calcitriol, calcipotriene, maxacalcitol, or paricalcitol to the skin can help treat plaque-type psoriasis. Applying vitamin D along with corticosteroids seems to work better than applying vitamin D or corticosteroids alone. But taking vitamin D by mouth doesn't seem to help.

Side Effects

When taken by mouth: Vitamin D is likely safe when taken in recommended amounts. Most people don't experience side effects with vitamin D, unless too much is taken. Some side effects of taking too much vitamin D include weakness, dry mouth, nausea, vomiting, and others. Taking vitamin D for long periods of time in doses higher than 4000 IU (100 mcg) daily is possibly unsafe and may cause very high levels of calcium in the blood.