Vitamin D Deficiency: What It Is, Symptoms, and How to Treat It

Overview

Vitamin D is a fat-soluble vitamin your body needs to absorb calcium, keep bones strong, support immune function, and regulate muscle and nerve health. Unlike most vitamins, your body can make vitamin D from sunlight, but many people don’t get enough from sun, food, or supplements alone. Vitamin D deficiency affects roughly 1 billion people worldwide, and is common across all age groups, especially in regions with little winter sun.

Signs & Symptoms

Many people with mild vitamin D deficiency have no obvious symptoms at all. As levels drop lower, you may notice the following issues:

• Fatigue and general weakness that doesn’t improve with rest
• Bone, joint, or muscle pain, especially in the back, legs, or ribs
• Frequent falls or difficulty getting up from a chair (common in older adults)
• Mood changes, including symptoms of depression or anxiety
• In children, soft or weak bones (rickets) that cause bowed legs, delayed growth, or dental problems

Causes & Risk Factors

Vitamin D deficiency happens when you don’t get enough of the vitamin, your body can’t absorb it properly, or your body converts it to its active form less efficiently. Common risk factors include:

• Limited sun exposure: staying indoors most of the time, wearing covering clothing for cultural or religious reasons, living in northern latitudes with little winter sun, or using sunscreen that blocks vitamin D production
• Dietary restrictions: vegan diets (few plant-based foods naturally contain vitamin D), lactose intolerance, or milk allergies that limit intake of fortified dairy
• Darker skin: higher melanin levels reduce the skin’s ability to make vitamin D from sunlight
• Older age: skin becomes less efficient at making vitamin D from sun, and kidneys are less able to convert it to its active form
• Medical conditions: Crohn’s disease, celiac disease, cystic fibrosis, or chronic kidney/liver disease that impair absorption or conversion of vitamin D
• Certain medications: including some anti-seizure drugs, glucocorticoids (steroids), and weight-loss medications that speed up vitamin D breakdown

Diagnosis

Vitamin D deficiency is diagnosed with a simple blood test that measures your 25-hydroxyvitamin D level, the most accurate marker of your vitamin D status. Your doctor will interpret your results based on guidelines from the Endocrine Society, and may also order tests for calcium, parathyroid hormone, or bone density if they suspect deficiency has already affected your bone health:

Treatment & Management

• Vitamin D supplements: Vitamin D3 (cholecalciferol) is the preferred form, as it matches the type your body makes from sun. Your doctor will recommend a dose based on your levels: mild deficiency may require 1,000–2,000 IU daily, while severe deficiency may need higher doses for a short period, followed by a lower maintenance dose. Vitamin D2 (ergocalciferol) is a plant-based option for vegans, though it is less effective at raising levels than D3.
• Dietary changes: Add vitamin D-rich foods to your diet, including fatty fish (salmon, mackerel, tuna), egg yolks, fortified cow’s milk, fortified plant-based milks (soy, oat, almond), fortified cereals, and UV-exposed mushrooms.
• Safe sun exposure: 10–30 minutes of midday sun on your arms, face, and legs 2–3 times per week is usually enough for most people with lighter skin. People with darker skin may need longer exposure. Always wear sunscreen after 10–15 minutes to reduce skin cancer risk, and avoid intentional sunburns.

Living With It

• Take a daily maintenance supplement as recommended by your doctor, usually 600–2,000 IU per day for most adults, with higher doses if you have risk factors like obesity or malabsorption disorders. This is the most important step to prevent recurrence of deficiency.
• Eat vitamin D-rich foods regularly, and choose fortified products (like milk, cereal, or plant-based milks) when possible.
• Get safe sun exposure when you can, especially in warmer months.
• Get your vitamin D levels checked every 1–2 years if you have risk factors, or as recommended by your doctor.
• Work with your doctor to manage any underlying medical conditions that affect vitamin D absorption, such as celiac disease or chronic kidney disease.