Supplementation signals: adults rarely lack of vitamin D, the lack of children and the elderly. Insufficient vitamin D in children will easily lead to calcium absorption obstacles, causing chicken breast and funnel chest; the lack of vitamin D in the elderly will easily lead to a decline in muscle strength and balance, easy to fall. Applicable people: children and the elderly. Expert analysis: children are in the developmental stage; the elderly indoor activities for a long time, less time in the sun, the body synthesizes vitamin D efficiency is not high, so it is easy to vitamin D deficiency. Human skin can synthesize vitamin D by itself after being exposed to sunlight, so it is still necessary for the elderly to spend an average of 20 minutes a day in the sun. To prevent UV burns, do it in the morning or at dusk when the sun is not too strong. Or take oral vitamin supplements, which can be taken once every few months as the body is able to store vitamin D. Signs of overdose: Vitamin D overdose can cause low-grade fever, vomiting, diarrhea, anorexia, and even soft tissue heterotopic ossification, proteinuria, and kidney damage. Foods rich in vitamin A: fish, animal liver, fruits and vegetables, including salmon, shrimp, milk, egg yolk, pig liver, mushrooms, orange juice, etc..