What You Need to Know About Vitamin D Deficiency

From keeping bones strong to supporting muscles and nerves to helping the immune system, vitamin D (also known as the 'sunshine vitamin') is a key player in maintaining your health. In fact, researchers are also looking into possible links between vitamin D deficiency (low levels of vitamin D) and other health conditions such as cancer, type 1 diabetes, heart disease, and multiple sclerosis, to name a few. And yet, about 25% of adult men and 35% of adult women in the U.S. are deficient in vitamin D.

What causes low vitamin D levels?

Vitamin D deficiency can be caused by several things, including:

Not getting enough vitamin D in your diet. Note that very few foods naturally contain vitamin D other than vitamin D-fortified foods (such as milk, breakfast cereals, and orange juice), so it can be tough to rely on your diet to get enough vitamin D.
Not getting enough sun exposure, because vitamin D is produced in the body when your skin is directly exposed to the sun. Still, dermatologists recommend using sunscreen and getting vitamin D from food and supplements to avoid the harmful effects from the sun’s ultraviolet rays.
The body not being able to absorb vitamin D from foods.
The liver or kidneys not being able to convert vitamin D to its active form in the body.
Taking medicines that affect vitamin D metabolism (e.g., steroids, certain anti-seizure medicines, HIV/AIDS medicines).

Who is at risk for vitamin D deficiency?

In addition, the following groups are at higher risk for vitamin D deficiency:

Older adults, because the skin becomes less efficient in producing vitamin D with age, and the kidneys are less able to convert vitamin D into its active form.
People who are obese or who have undergone gastric bypass surgery. In obese individuals, body fat binds to some vitamin D and prevents it from getting to the blood. In those who have had gastric bypass surgery, food or supplements bypass a section of the small intestine, reducing the ability to absorb vitamins, including vitamin D.
Breastfed infants, since human milk may not contain enough vitamin D to meet infant requirements.
People who have dark skin, because darker skin is less able to produce vitamin D from sunlight compared to those with lighter skin.
Those who have certain diseases such as Crohn’s disease or celiac disease, because the gut has a reduced ability to absorb fat from food. Note: vitamin D is a fat-soluble vitamin.

What are the signs and symptoms?

Many people with vitamin D deficiency do not experience symptoms until their vitamin D levels get very low. Some of the signs or symptoms of vitamin D deficiency may include:

Back or joint pain
Muscle weakness
Being very tired
Changes in mood
Depression
Problems falling asleep or staying asleep
Headache
Hair loss
Complications of a severe vitamin D deficiency (called rickets in children and osteomalacia in adults) can occur. These conditions can cause soft and weak bones and lead to bone fractures, muscle weakness, bone pain, and even permanent bone deformities if left untreated.

What should I do if I think I’m vitamin D-deficient?

Your healthcare provider can order a blood test, which can determine whether you have a vitamin D deficiency. If you have low levels of vitamin D and need to take a vitamin D supplement, ask your doctor or pharmacist about how much you need. The amount of vitamin D you need each day depends on factors such as your age, if you are pregnant or breastfeeding (for women), and if you are at high risk for a vitamin D deficiency.

Also keep in mind that while uncommon, it is possible to have too much vitamin D in your body usually from taking very high doses of vitamin D supplements. Signs of excess vitamin D include nausea, vomiting, poor appetite, feeling weak, confusion, and heart and kidney problems. Talk with your healthcare provider before taking a vitamin D supplement.

Richa Shah, PharmD, is a pharmacist completing a 2-year post-doctoral fellowship in Global Medical Information and Medical Affairs at Pfizer Inc.