◎Intern reporter Pei Chenwei

With the improvement of people's health awareness, many people began to pay attention to the supplement of various nutrients. On the Internet, many people said that they "don't spend enough time in the sun" and "bone density is not high enough", so they need to supplement vitamin D; But others believe that too much vitamin D supplementation "can be harmful to the liver."

What is the use of vitamin D for the human body? Who needs vitamin D supplementation, and how to supplement vitamin D scientifically and reasonably? With these questions, the Science and Technology Daily reporter interviewed relevant experts.

Vitamin D deficiency can cause a variety of diseases

Vitamin D is a fat-soluble vitamin that plays an important role in the body. "Vitamin D contributes to bone health, and the vitamin D endocrine system regulates the blood calcium balance and maintains normal blood calcium concentration." Rong Shuang, director of the Department of Nutrition and Food Hygiene of Wuhan University, vice chairman of the Nutrition and Neuroscience Branch of the Chinese Nutrition Society, and director of the Chinese Nutrition Society, told reporters.

Vitamin D is also involved in the regulation of various functions of the body. Rong Shuang said that vitamin D has the function of hormones, regulating the body's growth and development, cell differentiation, immunity, inflammation and so on through vitamin D receptors. "In recent years, a large number of studies have found that low vitamin D levels in the body are closely related to hypertension, tumors, diabetes, cardiovascular and cerebrovascular diseases, autoimmune diseases, etc., and are also related to the onset of some infectious diseases such as tuberculosis and influenza." Rong Shuang said.

Vitamin D deficiency is fairly common worldwide. Studies have shown that the global severe vitamin D deficiency rate is 15.7%, and the deficiency rate is 44.7%. The Scientific Research Report on Dietary Guidelines for Chinese Residents (2021) also pointed out that from 2016 to 2017, the rate of serum vitamin D deficiency in children and adolescents aged 6-17 in China was 18.6%; In 2015, vitamin D deficiency rates in adults aged 18 and over in China were 21.4%.

For most people, vitamin D deficiency can affect bone calcification, resulting in mineral abnormalities in bones and teeth. In addition, vitamin D deficiency can also cause different degrees of harm to people of different ages.

Vitamin D deficiency in infants and young children is not only prone to rickets, but also may cause softened and curved bones due to their inability to calcify normally, such as the formation of "X" or "O" shaped legs, sternum bulge, delayed fontanelle closure, pelvic narrowing and spinal curvature. At the same time, vitamin D deficiency often leads to poor abdominal muscle development in infants and young children, resulting in bulging abdomen; In terms of teeth, it is easy to lead to delayed teething, sparse and sunken caries and permanent teeth.

Pregnant women are prone to osteomalacia when they lack vitamin D, which is mainly manifested as osteomalacia, easy deformation, and pelvic deformation can cause dystocia.

Due to reduced liver and kidney function, poor gastrointestinal absorption, and reduced outdoor activities, vitamin D levels in older people are often lower than in younger people. Older people are susceptible to osteoporosis when vitamin D is deficient, which increases their risk of fractures.

Excessive vitamin D supplementation is not good for health

So, how to supplement vitamin D scientifically? "Regular sun exposure is the cheapest and most effective way to supplement vitamin D in the body. Spend 9-10 minutes in the sun every day at 4-5 a.m. or 10-20 p.m. Rong Shuang said, "As long as adults are exposed to sunlight regularly, the incidence of vitamin D deficiency can be greatly reduced." Vitamin D-fortified milk eaten in many areas of China can also improve vitamin D deficiency to a certain extent. "In terms of dietary supplementation, vitamin D is mainly found in animal foods such as liver and egg yolk of marine fish (such as sardines) and cod liver oil preparations. Rong Shuang reminds that human milk and ordinary milk are poor sources of vitamin D, and vegetables, cereals and their products and fruits also contain only a small amount of vitamin D, or almost no vitamin D.

It's important to note that vitamin D isn't "more is better." Rong Shuang said that although the toxic dose of vitamin D has not yet been determined, excessive intake of vitamin D may produce many side effects including lack of appetite, weight loss, nausea and vomiting and other symptoms, and develop into arterial, myocardium, lung, kidney, trachea and other soft tissue metastatic calcifications and kidney stones, severe vitamin D poisoning can lead to death.

"Vitamin D can be derived from the diet and synthesized by the skin, making it difficult to estimate dietary vitamin D supply." Rong Shuang said, "According to the dietary nutrient reference intake formulated in China, under the condition of sufficient calcium and phosphorus supply, the recommended intake of vitamin D for children, adolescents, adults, pregnant women, lactating mothers and the appropriate intake for infants aged 0-1 are 10 micrograms per day, and the recommended intake for the elderly over 65 years old is 15 micrograms per day; The tolerable maximum intake for people aged 11 years and older (including pregnant women and lactating mothers) is 50 micrograms per day, and the tolerable maximum intake for people aged 0-4 years, 4-7 years and 7-11 years is 20 micrograms, 30 micrograms and 45 micrograms per day, respectively. Rong Shuang said.