As the nutrient plays an important role in maintaining bone health, severe deficiency can show up as unexplained bone pain, shared Dr Sood. In his words, “Severe vitamin D deficiency can impair bone mineralisation, causing osteomalacia. This may produce deep aching or tenderness, particularly in the lower back, pelvis, hips, and legs.”

Significant vitamin D deficiency can cause proximal muscle weakness, particularly around the hips and thighs. “Everyday clues may include difficulty climbing stairs or getting up from a low chair,” noted the physician. “Correcting true deficiency can help, but extra vitamin D does not automatically increase strength.”

Dr Sood noted that low vitamin D has been associated with fatigue, potentially through muscle weakness, pain, or changes in cellular energy function. “One randomised trial found improved fatigue after treating deficient adults, although fatigue has many other possible causes,” he pointed out.

As Dr Sood explained, “Lower vitamin D levels are associated with depressive symptoms, but that does not prove deficiency causes depression. Trials suggest vitamin D may have a supportive role in some people with depressive symptoms, but it is not a replacement for appropriate mental health treatment.”

Prolonged severe deficiency can weaken bone through osteomalacia, reducing its ability to withstand normal mechanical forces. However, fractures can also reflect osteoporosis, training load, medications, or other bone disorders, cautioned Dr Sood.