Vitamin D Deficiency Linked to Muscle Loss and Fatigue in US Adults

A study of 11,242 U.S. adults aged 18 to 59 found that 42% were deficient in vitamin D and another 37.6% had insufficient levels. Participants with higher vitamin D concentrations had greater appendicular muscle mass, a relationship that remained after adjusting for race, season, age, activity and weight. Genetic analyses supported a causal link, especially pronounced in men.

Separate research highlights that vitamin D deficiency contributes to chronic fatigue by impairing mitochondrial energy production, sleep quality, muscle function and immune response. About 29% of U.S. adults are deficient, with an additional 41% falling below optimal levels. High‑risk groups include older or homebound individuals, people with darker skin, and those with gut disorders such as celiac disease or Crohn’s disease.