What Causes Vitamin D Deficiency?
Symptoms, risk factors and treatment options
Symptoms, risk factors and treatment options
Vitamin D — often called “the sunshine vitamin” — is an essential nutrient for good health. Your body produces it when your skin is exposed to UVB rays from sunlight. Despite its natural source, many people don’t get enough, which can lead to a deficiency that affects bones, muscles, mood and more.
Vitamin D plays several critical roles. It helps your body absorb calcium and maintain phosphorus levels. Both are vital for keeping your bones strong and healthy.
This important vitamin also supports your immune system and is linked to a lower risk of chronic conditions, including heart disease and diabetes. Yet, despite its importance, studies show more than 40% of Americans have vitamin D levels below what many experts consider optimal for overall health, and about 1 in 4 have levels considered deficient.
“Many people are surprised to learn how common vitamin D deficiency is — even here in sunny San Diego,” says Sally Williams, MD, an internal medicine physician at Scripps Clinic Torrey Pines. “Understanding your risk factors — talking to your doctor about whether testing is needed — can help you take simple steps to improve your health and prevent problems down the road.”
What causes vitamin D deficiency and who is at risk?
Common causes and risk factors:
Limited sun exposure: People living in northern areas with long winters or in cities with less sunlight often don’t get enough UVB rays. Those who work indoors, cover their skin for cultural or medical reasons or consistently use high-SPF sunscreen may block the skin’s ability to produce vitamin D.
Age: As we age, the skin’s ability to synthesize vitamin D from sunlight decreases significantly. Older adults often eat less and may stay indoors more, which can increase the risk of deficiency, weaken bones and raise the chance of fractures.
Skin tone: Individuals with darker skin have higher amounts of melanin, which naturally filters UVB rays. While this protects against sun damage, it also makes it harder for the body to generate adequate vitamin D, especially without regular sun exposure.
Health conditions: Chronic illnesses that impact digestion can reduce vitamin D absorption. This includes Crohn’s disease, celiac disease and inflammatory bowel disease. Obesity can also reduce vitamin D levels. Extra fat tissue stores vitamin D, making it less available to the body.
Medications: Long-term use of certain drugs, including anticonvulsants for seizure disorders and glucocorticoids for inflammatory conditions, can interfere with how your body processes and uses vitamin D, increasing the risk of deficiency over time.
If you fall into any of these groups, it’s a good idea to talk to your doctor about whether a blood test is right for you.
Most major medical organizations, including the U.S. Preventive Services Task Force and Endocrine Society, do not recommend routine vitamin D testing for everyone. Instead, they support targeted testing for those with symptoms or specific risk factors.
“These risk factors can quietly lower your vitamin D levels over time — even if you feel well,” Dr. Williams says. “If you’re at risk, your doctor may recommend a simple blood test to check your levels and help you decide on the next steps to protect your health.”
What are the symptoms of vitamin D deficiency?
Vitamin D deficiency symptoms can be subtle and overlap with other health conditions.
“Many patients don’t realize their symptoms, like fatigue or muscle pain, could be related to low vitamin D,” Dr. Williams notes. “That’s why testing can be so helpful if you’re at risk.”
Symptoms may include:
- Bone pain and muscle weakness
- Increased risk of bone fractures or bone deformities
- Fatigue, depression and anxiety
- Increased susceptibility to illness due to a weakened immune system
- Muscle cramps and general weakness, especially in athletes
If you have any of these symptoms or think you might be low in vitamin D, talk to your doctor.
How does vitamin D deficiency affect the body?
Vitamin D is essential for strong, healthy bones because it helps your body absorb calcium. When levels are too low, it can lead to osteomalacia in adults — a softening of the bones that increases fracture risk — or rickets in children, which causes bone deformities and weakness.
Beyond bone health, vitamin D also supports your immune system, improves muscle strength and plays a role in regulating mood.
Low vitamin D levels have been linked to a higher risk of:
- Depression and other mood disorders
- Multiple sclerosis
- Muscle injuries and slower recovery, especially in athletes
“For young athletes and active teens, maintaining good vitamin D and calcium levels is critical to prevent stress fractures and keep bones strong,” Dr. Williams adds.
How much vitamin D do you need?
Most adults need about 600–800 international units (IU) of vitamin D daily. Some people, depending on their health and test results, may need higher doses prescribed by their doctor.
Best sources of vitamin D
You can get the vitamin D your body needs from three main sources: sunlight, food and supplements.
Sunlight is the most natural and effective way. Spending 10 to 30 minutes in the sun several times a week helps your skin produce vitamin D. How much time you need depends on your skin tone, age and where you live. People in areas with limited sunlight, especially during winter, may need additional sources to maintain healthy levels.
Diet can also help you meet your needs. Try adding more vitamin D-rich foods to your meals, including:
- Fatty fish, such as salmon and mackerel
- Egg yolks
- Fortified milk, cereals and orange juice
- Sun-exposed mushrooms
Supplements are a safe and reliable option if sun and diet aren’t enough. “Supplements are safe and effective when taken as directed,” says Dr. Williams. “But it’s best to talk with your doctor before starting, since too much vitamin D can also cause problems.”
Taking more than the recommended amount of vitamin D can lead to vitamin D toxicity, which raises calcium levels in your blood and may cause nausea, fatigue, confusion or even kidney damage in severe cases. That’s why it’s important to work with your doctor to find the right dose for your needs.
How to treat vitamin D deficiency
If you’re diagnosed with vitamin D deficiency, your doctor will create a personalized treatment plan based on your needs and lifestyle. Treatment usually includes one or more of the following:
Increase safe sun exposure: Spending more time in sunlight helps your body produce vitamin D naturally. Your doctor can recommend what is appropriate for your skin type and health.
Eat more vitamin D-rich foods: Add fatty fish, egg yolks, fortified dairy and cereals and sun-exposed mushrooms to your diet.
Take supplements if needed: Your doctor may recommend daily or weekly supplements, sometimes at higher doses, to restore healthy levels.
“It’s important to follow your doctor’s guidance because the right dose varies for each person,” Dr. Williams emphasizes. “Too little won’t correct the deficiency and too much can lead to other health problems.”