Vitamin Deficiency in Adults: What to Know

What Is a Vitamin Deficiency?

A vitamin deficiency happens when your body does not get enough of a certain vitamin, and that shortfall leads to health problems. Your body needs 13 essential vitamins to function: A, C, D, E, K, and the B-complex vitamins (thiamine, riboflavin, niacin, pantothenic acid, biotin, vitamin B6, vitamin B12, and folate). Each one plays a distinct role, from supporting your immune system to keeping your nerves healthy.

Some vitamins are water-soluble (the B vitamins and vitamin C), meaning your body doesn't store them and you need to consume them regularly. Others are fat-soluble (vitamins A, D, E, and K), and your body can store them in fatty tissue and the liver. Because of these differences, the way a deficiency develops—and how quickly it appears—varies from vitamin to vitamin.

Sources: U.S. National Library of Medicine

Common Causes of Vitamin Deficiency

Vitamin deficiency can stem from a variety of causes, and often more than one factor is at play. Inadequate dietary intake is the most straightforward cause: if you regularly eat a diet that lacks a particular vitamin, your body's stores can run low over time. This can happen with restrictive eating patterns, such as a vegan diet that doesn't include reliable sources of vitamin B12, or simply because of a diet heavy in processed foods that are low in micronutrients.

But deficiency can also arise even when you eat well. Certain medical conditions interfere with the body's ability to absorb vitamins from food. For example, Crohn's disease and celiac disease can damage the gut lining and reduce absorption, and chronic kidney disease can affect vitamin D activation. Older adults are particularly vulnerable because the body's ability to absorb some vitamins, such as B12, declines with age, and appetite often decreases, leading to lower intake.

Medications can also play a role—long-term use of metformin or acid-suppressing drugs can lower vitamin B12 levels. Alcohol use is linked to deficiencies of thiamine (B1) and niacin (B3). Bariatric surgery, which changes how the body processes food, can increase the risk of thiamine and other deficiencies. Social isolation and reduced access to nutritious food are additional risk factors, especially for older adults. In some cases, a deficiency can develop even with a seemingly adequate diet because of underlying conditions that cause fat malabsorption, such as cystic fibrosis or short bowel syndrome, which particularly affect vitamin E.

Sources: Hackensack Meridian Health, AARP, American Family Physician (AAFP), Clinical Interventions in Aging (Dove Press), via PMC, BMC Research Notes via PMC

Overview of Deficiency Symptoms by Vitamin

The table below organizes common vitamin deficiencies and the symptoms reported in the sources. Symptoms can vary from person to person, and many overlap with other conditions. Use it as a starting point for a conversation with your healthcare provider, not as a self-diagnosis tool.

Vitamin Deficiency Symptoms Table

Sources: Pediatrics in Review / Stony Brook Medicine, American Family Physician (AAFP), Hackensack Meridian Health, Nutrients (MDPI), via PMC, Clinical Interventions in Aging (Dove Press), via PMC

Risk Factors for Vitamin Deficiency

Certain factors make it more likely you'll develop a vitamin deficiency. While anyone can be affected, some groups face higher risks.

• Dietary patterns: vegan or strict vegetarian diets can increase the risk of vitamin B12 deficiency; diets low in fruits, vegetables, and fortified dairy can lead to deficiencies in vitamin C, vitamin D, and others.
• Age: older adults are at higher risk because absorption declines and food intake often drops.
• Medical conditions: Crohn's disease, celiac disease, kidney disease, and conditions that cause fat malabsorption.
• Medications: long-term use of metformin or acid-suppressing drugs can affect vitamin B12.
• Alcohol use: chronic alcohol consumption can lead to deficiencies in thiamine and niacin.
• Pregnancy and breastfeeding: these increase the need for several vitamins and raise the risk of deficiency.
• Income and education: in the U.S., adults from low-income households and those without a high school diploma have a higher risk of deficiency.
• Bariatric surgery: this can affect absorption and increase the need for certain vitamins, including thiamine.

Sources: MDPI Nutrients, AARP, National Institute on Aging, BMC Research Notes via PMC

How Vitamin Deficiency Is Diagnosed

Vitamin deficiency is typically diagnosed through a combination of a medical history, a physical exam, and blood tests. Your doctor may ask about your diet, any underlying conditions, and symptoms you're experiencing. Blood tests can reveal whether you are lacking key nutrients, such as vitamin D, iron, or vitamin B12.

For vitamin B12 deficiency, doctors often start with a complete blood count and a serum vitamin B12 level. A level below 150 pg/mL is considered diagnostic. If your B12 level is normal or borderline but your doctor still suspects a deficiency, a test for serum methylmalonic acid can help confirm it.

For vitamin D, the standard test measures 25-hydroxyvitamin D in your blood. A normal range is often cited as 30 to 100 ng/mL, though specific cutoffs can vary by laboratory. If you have symptoms or risk factors for a deficiency, talk to your healthcare provider about whether testing is right for you.

Sources: American Family Physician (AAFP), GoodRx, Harvard Health Publishing

Treatment and Prevention Strategies

Treatment for a vitamin deficiency usually starts with correcting the shortfall, either through diet or supplements, depending on the cause and severity. For example, doctors often treat vitamin B12 deficiency with high-dose oral supplements (1 to 2 mg per day) or intramuscular injections. Oral treatment has been shown to be as effective as injections for correcting anemia and neurological symptoms, but injections may be used when symptoms are severe or when rapid improvement is needed.

For many people, adding vitamin-rich foods to the diet is enough to prevent deficiency. Most people can get the vitamins they need from food, and experts generally recommend a food-first approach. Vitamin D is harder to get from food alone, which is why your doctor may suggest a supplement if your blood level is low.

When you do take supplements, be aware that in the United States, dietary supplements are not regulated by the FDA in the same way that drugs are. Choosing a product that has been verified by a third party, such as a USP-verified supplement, can help ensure quality.

Sources: GoodRx, American Family Physician (AAFP), Hackensack Meridian Health, Harvard Health Publishing, National Institute on Aging

When to Seek Medical Help

If you have symptoms that could be related to a vitamin deficiency, it's important to see a healthcare provider for proper evaluation. Many deficiency symptoms are vague and can overlap with other conditions. Only a doctor can determine whether you actually have a deficiency and recommend the right treatment.

You should also seek medical help if you have risk factors for deficiency, such as an underlying digestive condition or a restrictive diet, and you're concerned about your nutrient status. Blood tests can give you a clear picture. Do not try to self-diagnose or treat a suspected deficiency with high-dose supplements without medical guidance, because some vitamins can be harmful in excess. Your healthcare provider can help you find the safest and most effective way to address any gaps.

Sources: Harvard Health Publishing, National Institute on Aging