Vitamin D deficiency symptoms

Vitamin D deficiency is the most common micronutrient gap in the United States — estimates suggest up to 40% of adults have levels below the clinical cutoff. Because vitamin D acts more like a hormone than a vitamin, shortfalls can show up across mood, energy, bone health, and immune function. Here are the patterns most commonly associated with low vitamin D, what drives them, and when it is worth testing.

Common symptoms associated with low vitamin D

• Persistent fatigue — even with adequate sleep.
• Low mood or seasonal low mood — particularly in fall and winter.
• Bone aches and muscle aches — dull, diffuse, often in the low back, hips, or thighs.
• Muscle weakness — difficulty climbing stairs or rising from a chair.
• Frequent colds or infections — vitamin D modulates innate immunity.
• Hair shedding — diffuse thinning associated with severe deficiency.
• Slow wound healing.

These are nonspecific — meaning they overlap with thyroid issues, depression, iron deficiency, and chronic stress — so clinical confirmation via a 25-hydroxyvitamin D blood test is the reliable way to know.

Food sources and sunlight

Very few foods contain meaningful vitamin D. Sunlight drives the bulk of natural production in the skin, which is why northern latitudes, indoor work, and sunscreen use raise deficiency risk. Dietary sources per the NIH Office of Dietary Supplements include:

• Fatty fish — salmon, mackerel, sardines, trout (≈400-700 IU per serving)
• Cod liver oil (≈1,300 IU per tablespoon)
• Egg yolks (≈40 IU each, varies with hen diet)
• Fortified milk, orange juice, and cereals (≈100 IU per serving)
• Some mushrooms exposed to UV light

Adult RDA is 600 IU/day (800 IU/day after 70), but many clinicians target higher serum levels via supplementation, especially in winter.

Who is at higher risk

• People living above ~37° latitude (roughly north of San Francisco / Washington, DC)
• Darker skin tones — melanin reduces cutaneous vitamin D synthesis
• Indoor workers, shift workers, and older adults
• Regular sunscreen users (SPF 30+ blocks ~95% of UVB)
• Obesity — vitamin D is sequestered in adipose tissue
• Malabsorption conditions — celiac, Crohn's, bariatric surgery
• Chronic kidney or liver disease (affects activation)
• Exclusively breastfed infants not receiving supplementation

When to test and see a doctor

Ask for a 25-hydroxyvitamin D (25-OH D) serum test if you have several of the symptoms above, belong to a higher-risk group, or have unexplained bone/muscle pain. Most labs report sufficiency at ≥30 ng/mL (≥75 nmol/L), with deficiency under 20 ng/mL. Your clinician can recommend a loading dose or daily maintenance depending on how low the reading is.

Educational content only. This guide does not diagnose, treat, prescribe, or replace clinician judgment. If you are pregnant, breastfeeding, on prescription medications, or have a medical condition, consult a qualified healthcare professional before starting any supplement.