Rickets is caused by deficiency of which vitamin?

• A. B1
• B. C
• C. niacin
• D. D

Answer: (D)

Rickets results from not having enough vitamin D, which is needed for absorbing calcium and phosphate and for properly mineralizing bone as it grows. Without sufficient vitamin D, bones remain soft and poorly mineralized, leading to the characteristic deformities seen in children, such as bowed legs. Vitamin D comes from sun exposure and certain foods, and its deficiency can also cause secondary hyperparathyroidism, further compromising bone mineralization. The other vitamins listed regulate different bodily processes—B1 in energy metabolism, C in collagen synthesis and connective tissue health, and niacin in various metabolic pathways—so they do not produce the bone-mineralization defects seen with vitamin D deficiency. Therefore, the vitamin whose deficiency causes rickets is vitamin D.