Am I Vitamin D Deficient? Signs of Low Vitamin D in Adults

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Vitamin D plays a critical role in your bone health and overall wellness. But millions of Americans don’t get enough.

A 2025 analysis in The American Journal of Clinical Nutrition reported that over 20% of U.S. adults were at risk of vitamin D insufficiency or deficiency. Other studies have reported even higher totals of vitamin D deficiency and insufficiency.

Vitamin D deficiency can cause many health problems. In adults, it can lead to osteoporosis, putting you at risk of bone fractures.

Low vitamin D signs can be subtle. But it’s important to stay on top of your vitamin D intake. Here are ways adults can support healthy vitamin D levels, and how to know if your vitamin D is low.

What Is Vitamin D?

Vitamin D is a fat-soluble vitamin. Your body makes it naturally when exposed to sunlight. You can also get it from other sources, such as diet and supplements.

Why Is Vitamin D Good for You?

Vitamin D’s biggest health benefit is for your bones. It helps your body absorb calcium, which helps maintain healthy bones. It can also prevent conditions like rickets in children and osteoporosis in adults.

But its benefits go beyond the bones. Vitamin D helps your immune system fight off pathogens like bacteria and viruses. It also helps your muscles move, and your nerves carry messages from the brain to the rest of the body.

Researchers have also studied vitamin D’s impact on preventing or reducing many medical conditions, including:

• Certain cancers.
• Depression.
• Heart disease.
• Multiple sclerosis.
• Type 2 diabetes.

There’s a mix of findings about vitamin D’s impact on these conditions.

How Much Vitamin D Should You Get Per Day?

How much vitamin D you need depends on how old you are. The daily recommended amounts are:

• Newborns to 12 months — 10 micrograms (mcg) or 400 international units (IU) per day.
• Children and adults 1 to 70 years old — 15 mcg or 600 IU per day.
• Adults 71 and older — 20 mcg or 800 IU per day.

If you’re pregnant or breastfeeding, you should have 15 mcg or 600 IU of vitamin D daily.

How Do You Get Vitamin D?

The two natural ways of getting vitamin D are sunlight and diet.

Vitamin D and sunlight

There’s a reason vitamin D is sometimes called “the sunshine vitamin.” Sunlight on exposed skin helps your body produce vitamin D.

But sunlight alone often isn’t enough for people to get the amount of vitamin D they need. Many people live in climates with reduced sunlight in parts of the year. That can prevent vitamin D activation during those times.

Older adults and people with darker skin tones also don’t produce as much vitamin D from the sun. Other people may spend the bulk of their time indoors, preventing them from getting vitamin D from the sun.

It’s also important to note that too much exposure to the sun can cause skin cancer and other skin damage. Using sunscreen and wearing protective clothing can affect how much vitamin D you get from the sun. But those preventive steps are also crucial to protecting yourself from skin cancer and other sun damage.

You should wear a broad-spectrum sunscreen with a sun protective factor (SPF) of at least 15 when exposed to the sun.

Do you need sunlight for vitamin D?

Sunlight is one source of vitamin D, but it’s not the only source. You can also get it through diet and supplementation.

Vitamin D and your diet

You can also get vitamin D from your diet. Vitamin D occurs naturally in a few types of food, including:

• Beef liver.
• Egg yolks.
• Fatty fish (such as mackerel, salmon, trout, and tuna).
• Fish liver oils.
• Mushrooms.

Many other foods and drinks are “fortified” with vitamin D, meaning they have vitamin D added. Examples of vitamin D-fortified foods include:

• Breakfast cereals.
• Cow’s milk (and many plant-based milks).
• Infant formula.
• Orange juice.
• Margarine.
• Yogurt.

If you’re unsure, talk to your doctor about the best foods with vitamin D for adults and children.

Who’s at Risk for Vitamin D Deficiency?

Vitamin D deficiency occurs if you don’t get enough through natural sources or if your body can’t make or use it correctly. Although a Vitamin D deficiency can happen to anybody, certain groups are more at risk, including:

• Breastfed infants.
• Older adults.
• People who are obese or have had weight loss surgery.
• People on certain medications, such as cholesterol-lowering drugs, steroids, and weight loss medications.
• People with darker skin.
• People with limited sun exposure.
• People with medical conditions that affect their body’s ability to absorb vitamin D, such as celiac disease, Crohn’s disease, cystic fibrosis, or ulcerative colitis.
• People with chronic kidney or liver disease.

What Are the Symptoms of Vitamin D Deficiency?

The signs of low vitamin D in adults and children can be hard to spot. Many are general, nonspecific symptoms, but some potential signs of vitamin D deficiency include:

• Bone pain.
• Fatigue.
• Lower back pain.
• Mood changes.
• Muscle aches.
• Muscle weakness.

Over time, vitamin D deficiency can lead to serious complications, including:

• Hypocalcemia — Low levels of calcium in the blood.
• Hypophosphatemia — Low levels of phosphate in the blood.
• Osteomalacia — Softened bones in adults.
• Rickets — Softened bones in children.

These conditions are rare in the United States, largely due to fortified foods. In adults, vitamin D deficiency can lead to lower bone density (osteoporosis), putting them at greater risk of falls and fractures.

How Is Vitamin D Deficiency Diagnosed?

Doctors can diagnose vitamin D deficiency through blood testing and/or x-rays.

Vitamin D testing isn’t a typical adult preventive wellness test. But your provider may order it if you have signs of vitamin D deficiency or complications.

How Is Vitamin D Deficiency Treated?

If you have vitamin D deficiency, your provider can offer treatment options. They may recommend you get more vitamin D through your diet and sunshine (while staying properly protected). But the most common treatment for vitamin D deficiency is supplementation.

According to a 2023 report from the Centers for Disease Control and Prevention (CDC), 18.5% of U.S. adults take a vitamin D supplement. Vitamin D supplements come in many different strengths. Because vitamin D is fat-soluble, it’s best taken with food.

Providers often recommend vitamin D supplementation for breastfed babies because breast milk contains little vitamin D. Infant formula comes fortified with vitamin D, but your child’s provider may still recommend vitamin D supplementation.

It’s important to talk to your provider before starting vitamin D or any other supplement. That way, you can avoid any potential risks.

Is It Possible to Have Too Much Vitamin D?

Yes, you can have too much vitamin D — and it can be harmful to your health. Excess vitamin D can lead to high amounts of calcium in your body, which can be harmful.

Your body controls the amount of vitamin D you make from the sun, but you can get excess vitamin D from supplements. That makes it important to stay in touch with your provider about your vitamin D supplement use. It’s also why you shouldn’t start taking a supplement without medical guidance.

Symptoms of excess vitamin D intake include:

• Confusion.
• Constipation.
• Excess thirst.
• Excess urination.
• Kidney stones.
• Loss of appetite.
• Muscle weakness.
• Nausea and vomiting.
• Weight loss.

Vitamin D can also interact with certain medications, which can also cause problems.

Over time, having too much vitamin D can damage your kidneys and heart. You can also die from excess vitamin D.

If you’re concerned about your vitamin D levels — whether they’re too high or low — talk to your medical provider. They can order vitamin D testing and provide evidence-based vitamin D guidance.