Vitamin D Deficiency: Causes, Who Is at Risk and What It Does

Vitamin D deficiency means your body isn't getting enough vitamin D to stay healthy. Vitamin D helps the body absorb calcium, one of the main building blocks of bone, and plays a part in the nervous, muscle and immune systems. You can get it three ways: through your skin, which makes it after exposure to sunlight; from your diet; and from supplements. Because too much sun can age the skin and cause skin cancer, many people rely on the other two.

How much you need

People at high risk of deficiency may need more; check with your health care provider.

Causes

• Not getting enough vitamin D in your diet.
• Not absorbing enough from food (malabsorption).
• Not getting enough sunlight.
• Liver or kidneys that cannot convert vitamin D into its active form.
• Medicines that interfere with converting or absorbing it.

Who is at higher risk

• Breastfed infants, because human milk is a poor source of vitamin D. If you are breastfeeding, give your baby a 400 IU vitamin D supplement every day.
• Older adults, whose skin makes vitamin D from sunlight less efficiently and whose kidneys convert it less well.
• People with dark skin, which makes less vitamin D from sun.
• People with conditions that hinder absorbing nutrients, such as Crohn's disease, ulcerative colitis and celiac disease.
• People with obesity, whose body fat binds some vitamin D and keeps it from the blood.
• People who have had gastric bypass surgery, which bypasses part of the small intestine where vitamin D is absorbed.
• People with chronic kidney or liver disease.
• People taking medicines that affect vitamin D, including some cholesterol, anti-seizure, steroid and weight-loss medicines.

If you are at risk, talk to your provider; a blood test can measure your vitamin D level.

What deficiency does

Deficiency can reduce bone density, contributing to osteoporosis and fractures. Severe deficiency can cause:

• rickets in children — a rare disease in which bones become soft and bend; African American infants and children are at higher risk;
• osteomalacia in adults — weak bones, bone pain and muscle weakness.

Getting more vitamin D

A few foods contain some naturally: fatty fish such as salmon, tuna and mackerel; beef liver; cheese; mushrooms; and egg yolks. Others have it added — check the label — often milk, breakfast cereals, orange juice, yogurt and other dairy products, and soy drinks. It is also in many multivitamins and in vitamin D supplements, including a liquid for babies. Deficiency is treated with supplements; ask your provider how much, how often and for how long.

Too much vitamin D

Too much vitamin D — vitamin D toxicity — is harmful, and usually comes from overusing supplements. Signs include nausea and vomiting, poor appetite, constipation, weakness and weight loss. Very high levels can damage the kidneys and raise blood calcium (hypercalcemia), which can cause confusion, kidney failure and an irregular heartbeat. Sun exposure cannot cause toxicity, because the skin limits how much vitamin D it makes.

Sources

• MedlinePlus, U.S. National Library of Medicine, "Vitamin D Deficiency." https://medlineplus.gov/vitaminddeficiency.html
• Rewritten in hubnx's own words.