Vitamin D has long been known as an essential nutrient for strong bones and teeth, but in recent years it has gained a new reputation as a “longevity” vitamin because of its wide-reaching role in supporting healthy aging, from brain health and muscle strength to immune resilience and overall vitality.
Vitamin D’s link to longevity is also due to large population studies that found adults with low vitamin D levels are more likely to die earlier, especially from heart disease and cancer, than people whose levels fall in the normal range, says registered dietitian Liz Weiss of Liz’s Healthy Table.
However, vitamin D is also one of the nutrients most likely to be lacking in the American diet. If you think you may not be getting enough vitamin D, learn more about why you need this nutrient, signs of a deficiency and how to easily boost your daily intake.
[Read: New Dietary Guidelines for Americans 2025-2030: Reimagining the Food Pyramid]
Vitamin D Benefits: Why This Nutrient Is Important
Vitamin D is a hard-working nutrient that significant health benefits and multiple functions, including:
— Supports strong bones and teeth by helping the body absorb calcium and phosphorus
— Helps prevent osteoporosis and reduce fracture risk, especially in aging
— Supports immune health and helps control infections.
— Reduces inflammation
— Regulates blood sugar levels
— Plays a role in muscle strength and balance
— Supports mood and brain health
— May reduce the risk of autoimmune diseases, such as rheumatoid arthritis and psoriasis.
[Vitamin Deficiency: Common Symptoms to Watch For]
How Much Vitamin D Do You Need?
The amount of vitamin D you need each day depends on your age. You’ll see vitamin D listed as international units (IU) and micrograms (mcg). The Recommended Dietary Allowance, or RDA, for vitamin D is 600 IU or 15 mcg for children and young adults. After age 70, the RDA increases to 800 IU or 20 mcg per day.
Other experts suggest we need even more vitamin D. For example, the Endocrine Society recommends adults ages 75 and older may benefit from exceeding the RDA to potentially lower mortality risk.
Recommended daily amounts of vitamin D by age
| AGE GROUP | VITAMIN D PER DAY |
| 0-12 months | 10 mcg/400 IU |
| 1-70 years | 15 mcg/600 IU |
| 70+ years | 20 mcg/800 IU |
[SEE: Best Vitamins and Minerals for Older Adults.]
Signs of Vitamin D Deficiency
You may not always have symptoms with a vitamin D deficiency. However, these are some of the early signs:
1. Persistent fatigue
2. Mood changes
3. Bone pain
4. More frequent infections and illnesses
5. Muscle twitching, weakness or pain
6. Joint stiffness or arthralgias
7. Lower back pain
Potential Complications of Low Vitamin D
If vitamin D deficiency continues for long periods, it may result in complications. Low blood levels of vitamin D have been associated with the following:
— Bone fragility and osteoporosis
— Falls and fractures
— Increased risk of death from cardiovascular disease
— Cognitive impairment in older adults
— Pregnancy complications
— Certain cancers, including breast, prostate and colon
[READ: How Much Sun Do You Need for Vitamin D?]
Vitamin D Deficiency Causes
What can lead to a vitamin D deficiency?
| Cause | How |
| Dietary choices | Few foods are naturally good sources of vitamin D, which makes it more difficult to consume adequate amounts. |
| Environment |
Certain environmental factors could give your body less opportunity to produce vitamin D from UV light exposure: — Lack of outdoor activity — Using sunscreen — Living farther away from the equator |
| Medical conditions |
Certain medical conditions may interfere with vitamin D absorption, including: — Ulcerative colitis — Cystic fibrosis |
| Surgery | Weight loss surgeries like gastric bypass surgery make it difficult to absorb sufficient quantities of vitamin D. |
| Medication |
Some medications can lower vitamin D levels, including: — Cholesterol-lowering drugs — Steroids — |
Who Is at Risk of Low Vitamin D?
Vitamin D is naturally found in only a handful of foods, and many people don’t eat those foods very often, says Weiss.
“At the same time, our bodies rely on sunlight to make vitamin D, but factors like living in northern climates, spending more time indoors, wearing sunscreen and aging skin all reduce how much we produce,” she explains. “As a result, falling short on vitamin D is common, especially as we get older.”
Here are the factors that may determine your risk:
— Age. The skin’s ability to make vitamin D when exposed to sunlight declines as you age. This is one reason why higher vitamin D amounts are recommended for adults over age 70. Infants are also at risk of not getting enough vitamin D, especially breastfed babies since breast milk contains only a small amount of vitamin D compared to infant formula, which is fortified with vitamin D.
— Mobility. People who are homebound or rarely go outside, such as those who are hospitalized or in nursing homes, may not be able to use sun exposure as a source of vitamin D.
— Skin color. The darker your skin, the less vitamin D you make from sunlight exposure. For example, African Americans and Hispanic people tend to have lower vitamin D levels.
— Weight. A body mass index of 30 or greater is considered a risk factor. Some of the vitamin D can bind to body fat instead of getting into the bloodstream.
— Restricted diets. People who are vegan or follow a 100% plant-based diet may struggle to get enough vitamin D because many of the best sources of vitamin D are from animals, such as dairy and fish.
Best Sources of Vitamin D
To increase daily vitamin D, there are four main sources:
— Foods naturally rich in vitamin D. Fatty fish like salmon and tuna, egg yolks, beef liver, cod liver oil and mushrooms that have been exposed to UV light in the growing process are naturally rich in the vitamin.
— Supplements. Vitamin D supplements can help ensure you’re getting adequate amounts each day. Vitamin D3 or cholecalciferol is the preferred form.
— Sunlight. About 20 minutes of unprotected sun exposure each day will help your body make adequate amounts of vitamin D.
— Vitamin D fortified foods. Dairy and non-dairy milk, orange juice and breakfast cereals are sometimes fortified with vitamin D.
“Because vitamin D fortification varies by product and brand, it’s important to read labels to see how much you’re actually getting,” says Weiss.
When to See a Doctor
If you have these signs and suspect they’re linked to a vitamin D deficiency, talk to your healthcare provider about getting a blood test that can check for vitamin D levels.
The most accurate way to measure vitamin D levels is the 25-hydroxyvitamin D blood test. A vitamin D level less than 20 nanograms/milliliter (ng/mL) is generally accepted as deficient. However, some groups define vitamin D deficiency as less than 30 ng/mL
Even though there’s been increased attention on vitamin D deficiencies — and an estimated 10 million vitamin D blood tests are performed annually — the U.S. Preventive Services Task Force found insufficient evidence to recommend widespread vitamin D testing among healthy adults.
Only high-risk populations are recommended for vitamin D screening, including:
— Nursing home residents
— Hospitalized patients
— Adults over 65
— Women with osteoporosis
— African American and Hispanic individuals
— People with chronic kidney disease, chronic liver disease and malabsorption syndromes
What to Do If You’re Vitamin D Deficient
If a lab test reveals low levels of vitamin D, your healthcare provider may recommend supplementation. The safe upper limit for vitamin D supplementation is 4,000 IU or 100 mcg per day, so it’s important not to go over that amount unless recommended by your doctor.
Don’t expect miracles by taking more vitamin D. Even though vitamin D is an essential nutrient, more isn’t always better.
Dr. JoAnn Manson, chief of preventive medicine at Brigham and Women’s Hospital in Harvard Medical School and leader of a large vitamin D randomized trial called VITAL, found that increasing vitamin D did not protect against fractures, heart disease or cancer.
“We only need small to moderate amounts of vitamin D, and among the healthy population, most people do not need screening tests or supplements,” she says. “Larger amounts do not confer greater benefits.”
High doses of vitamin D, however, may benefit the immune system and tamp down inflammation, Manson says. That may be why the VITAL trial found that vitamin D helped lower the risk of autoimmune conditions, such as rheumatoid arthritis and psoriasis, she says.
Vitamin D Supplement Side Effects
Unlike vitamins C and B, which are water-soluble vitamins, vitamin D is a fat-soluble vitamin (along with vitamins A, E and K). This means that vitamin D can be stored in the body and could pose a risk for toxicity when consumed in large amounts.
With the growing consumer interest in vitamin D — and the articles and books extolling the benefits — there’s actually been an increase in vitamin D toxicity. Some of the cases are due to errors, yet much of the blame is due to the widespread availability of high-dose, over-the-counter supplements.
Taking 60,000 IU of vitamin D per day for several months has been shown to cause toxicity. The main consequence is a buildup of calcium in your blood, called hypercalcemia, which can cause several problems:
— Nausea and vomiting
— Abdominal pain
— Confusion
— Weakness
— Poor appetite
— Constipation
Vitamin D toxicity could progress to kidney failure and irregular heartbeat or arrhythmias. As always, check with your doctor before taking vitamin D supplements.
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Signs of Vitamin D Deficiency originally appeared on usnews.com
