Lifestyle

Doctors Say 42% of Americans Are Vitamin D Deficient and Most Have No Idea

By Curtis Jones · July 8, 2026

Approximately 42% of American adults are deficient in vitamin D, according to research published in the journal Nutrition Research. The prevalence is higher in older adults, people with darker skin, and anyone who spends most of their time indoors. The symptoms are so easy to attribute to aging or stress that most deficient adults never connect them to a vitamin.

1. Bone and joint pain that seems to come from nowhere

Vitamin D is essential for calcium absorption. Without adequate levels, bones weaken gradually — a process that produces a dull, diffuse aching in the bones and joints that feels different from arthritis or injury pain. It’s often worst in the lower back, pelvis, and legs. People describe it as “everything just aches” — and they attribute it to aging or overuse.

2. Fatigue that doesn’t improve with more sleep

Low vitamin D levels have been associated with persistent fatigue in multiple clinical studies. The mechanism involves vitamin D’s role in mitochondrial function — the energy-producing process inside every cell. When levels drop, cellular energy production becomes less efficient. The fatigue is systemic and does not respond to additional sleep, caffeine, or rest.

3. Muscle weakness — particularly in the legs

Difficulty standing from a seated position, trouble climbing stairs, or a general feeling of weakness in the legs can indicate vitamin D deficiency. The vitamin plays a direct role in muscle fiber function. Weakness from deficiency is distinct from deconditioning — it develops even in people who are otherwise active.

4. Frequent colds, infections, or slow healing

Vitamin D supports immune function by activating T cells — the immune cells that identify and destroy pathogens. People with low vitamin D levels get sick more frequently, stay sick longer, and heal from cuts and wounds more slowly. If you catch every cold that circulates and your recovery takes longer than it used to, vitamin D is one of the first levels worth checking.

5. Low mood or seasonal depression that extends past winter

The association between vitamin D and mood is well established — seasonal affective disorder is partly driven by reduced sunlight exposure and the corresponding drop in vitamin D production. But deficiency-related mood changes aren’t limited to winter. People who work indoors, wear sunscreen consistently, or live in northern latitudes can be deficient year-round — and the low mood that comes with it persists through spring and summer.

The screening is a simple blood test — a 25-hydroxyvitamin D level — available at any primary care visit. Optimal levels are 30 to 50 ng/mL. Below 20 ng/mL is considered deficient. Below 12 ng/mL is severely deficient. If you’re over 50 and experiencing multiple symptoms on this list, ask for the test at your next appointment. Supplementation is inexpensive — typically $5 to $15 per month — and the improvement in symptoms can be significant within 6 to 8 weeks.