Vitamin D3
Redirected from "Cholecalciferol"
Also known as: Cholecalciferol
Vitamin D3, or cholecalciferol, is a fat-soluble vitamin that the skin can produce when ultraviolet B radiation reaches it. The liver and kidneys convert vitamin D through several steps into biologically active compounds. These help regulate calcium and phosphate balance and support normal bone, muscle, nerve, and immune function. Vitamin D3 is a nutrient and hormone precursor, not a muscle-building supplement in itself.
Vitamin D3 occurs naturally in relatively few foods, particularly fatty fish and egg yolk, and may be added to fortified foods. Vitamin D2, or ergocalciferol, is another supplement and food-fortification form. Both can raise vitamin D status, although D3 often produces a larger or more sustained rise. Sun exposure also contributes, but production varies with season, latitude, skin pigmentation, age, clothing, and sunscreen use. Deliberate unprotected ultraviolet exposure is not a risk-free supplementation strategy.
Vitamin D status is usually assessed with a blood concentration of 25-hydroxyvitamin D, written 25(OH)D. Interpretation is not based on vague symptoms alone, and professional bodies do not use identical thresholds for every purpose. Low status is more likely when sun exposure is limited, skin synthesis is reduced, dietary supply is low, or fat absorption is impaired. The NIH vitamin D fact sheet and German Nutrition Society reference guidance distinguish physiological need from claims made for high-dose products.
A supplement can correct inadequate intake or deficiency, but the expected benefit depends strongly on starting status. Across 11 randomized trials involving 436 athletes, a 2023 systematic review and meta-analysis found no statistically significant effect of vitamin D supplementation on maximal strength or power; the authors noted important limitations and called for further research. A universal dose is therefore inappropriate: age, diet, sun exposure, laboratory findings, health conditions, and prescribed treatment can change what is suitable. The amount on a label may be stated in micrograms or international units, so those units should not be treated as interchangeable numbers.
Excess vitamin D from supplements can cause abnormally high blood calcium and lead to nausea, weakness, kidney problems, or heart-rhythm disturbances; this is different from ordinary food intake or sun exposure. High-dose or long-term use deserves particular caution with kidney disease, disorders of calcium metabolism, or medicines that affect vitamin D or calcium. Vitamin D3 is also commonly sold together with vitamin K2, but K2 is not an automatic requirement with every D3 dose. Whether either supplement is indicated is a separate question from the fact that both nutrients participate in bone physiology.