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Vitamins have many functions. They help regulate metabolism, convert fat and carbohydrates into energy, and aid in the formation of healthy bones and tissues. They do not prevent or cure diseases such as cancer or other aging-related disorders. However, they may help fortify the immune system and provide protection against some illnesses. All naturally occurring vitamins are found only in plants and animals. With a few exceptions, the human body cannot manufacture its own vitamins; they must be obtained from food or supplements. In general, the best way to get the vitamins you need is by eating a healthy diet.


Folate plays an essential role in making new body cells. It also works with vitamin B12 to form hemoglobin in red blood cells and may protect against heart disease. Folate deficiency may result in a type of anemia. Pregnant women who do not get adequate folate early in pregnancy have a greater risk of having a baby with neural tube defects, which are birth defects of the brain and spinal cord. One example of a neural tube defect is spina bifida—a condition in which the bones of the spinal column do not close completely around the developing nerves of the spinal cord, which may lead to permanent nerve damage. Too much folate may mask a B12 deficiency. Folate may also interfere with certain medications.

Vitamin K

Vitamin K is important for the body’s normal production of some clotting factors. The main source of vitamin K is the diet, particularly green leafy vegetables. A smaller amount is produced in the gut by certain bacteria. Prolonged use of antibiotics can destroy some of the intestinal bacteria that produce vitamin K. If a deficiency does occur, blood will not clot properly. People with bleeding disorders could become deficient in vitamin K if they are malnourished, which can result in an increase in bleeding episodes.

Vitamin C

Vitamin C helps produce collagen, a connective tissue that holds muscles, bones, and other tissues together. It also helps keep blood vessels firm, protecting the body from bruising. It helps the body absorb the iron and folate we get when we eat plant-based foods, keeps gums healthy, helps heal cuts and wounds, protects against infection, and acts as an antioxidant. Vitamin C deficiency may lead to scurvy. Typically, excess amounts of vitamin C, which is a water-soluble vitamin, are excreted in urine. This can, however, distort the results of urine tests for diabetes and diabetes-related kidney disease and severe hyperglycemia. Mega-doses of vitamin C can cause kidney stones or diarrhea.

Vitamin A

Vitamin A promotes normal vision and the growth and health of the body’s cells and tissues. It works as an antioxidant to possibly reduce the risk of certain cancers and some diseases of aging. Vitamin A deficiency may lead to eye problems; dry, scaly skin; reproductive problems; and poor growth. Excess amounts are stored in the body and can be harmful over time, and can result in headaches, liver damage, bone and joint pain, abnormal bone growth, nerve damage, and birth defects.

Vitamin E

Vitamin E works as an antioxidant. It may help prevent the oxidation of LDL cholesterol (low-density lipoprotein, or "bad" cholesterol) and, in turn, lower the risk of heart disease and stroke. Vitamin E deficiency is rare, although people with poor fat absorption, such as preterm infants and people with cystic fibrosis, may be at risk since vitamin E is fat soluble. An excess amount may impair the action of vitamin K and increase the effect of anticoagulant medication. In people with bleeding disorders, it may worsen their bleeding symptoms.

Vitamin D

Vitamin D is important for maintaining bone health. Vitamin D helps the body absorb calcium. The human body is always breaking down old bone and building new bone. The body uses calcium during the building of this new bone to give it strength and mass. Osteoporosis, which is the thinning of bones, occurs when more old bone material is broken down than new bone material is created. Osteoporosis can result in fractures and other serious injuries from falls.

In addition to vitamins and supplements, vitamin D can be obtained through foods such as salmon, tuna, sardines, and fortified milks and juices. Vitamin D, known as the "sunshine vitamin," can also be absorbed through the skin as a result of sun exposure.

People with hemophilia appear to be susceptible to poor bone health, possibly because of the effects of joint bleeds. During a bleed, blood flows into the joint capsule. Recurring bleeds can lead to the erosion of bone cartilage associated with the target joint.

Individuals who also have HIV are susceptible to bone loss and fractures as a result of the use of certain anti-HIV medications.

Excess amounts of vitamin D stored in the body can be toxic and could lead to kidney stones or weak bones.

Talk with your health care provider before taking any vitamins or supplements.