Vitamin A (Retinol), Serum

Vitamin A is a nutrient your body needs for healthy vision (especially in low light), a strong immune system, and maintaining healthy skin and tissues. Your blood level of vitamin A (called retinol) can be measured to check whether you are getting too little or too much. Too little vitamin A can cause difficulty seeing at night, increased infections, and in severe cases, eye damage. Too much—usually from high-dose supplements rather than food—can be harmful to the liver and bones, and is especially dangerous during pregnancy. Your doctor will interpret your result alongside your diet, health history, and other lab values.

When elevated: Elevated serum retinol may indicate vitamin A toxicity (hypervitaminosis A), which can manifest as hepatotoxicity, pseudotumor cerebri, bone pain, alopecia, and teratogenic risk in pregnancy. Chronic excess is associated with reduced bone mineral density and increased fracture risk. When low: Low serum retinol is associated with night blindness (nyctalopia), xerophthalmia, increased susceptibility to infections (particularly measles and respiratory infections), impaired growth in children, and poor wound healing. Severe deficiency can progress to corneal ulceration and irreversible blindness.

Vitamin A supports immune function and epithelial repair, which can be stressed by intense training and environmental exposure. Adequate status may help maintain mucosal barriers and reduce upper-respiratory infection risk during heavy training blocks, though serum retinol alone is an insensitive marker of total body stores.