What Are Topical Retinoids?

A fat-soluble vitamin that is stable to heat, acids, and bases, and is easily oxidized. Ultraviolet rays can promote its oxidative damage. Vitamin A includes A1 and A2, A1 is retinol. Vitamin A2 is 3-dehydroretinol, and its physiological activity is 40% of Vitamin A1. ^[1]

Vitamin A was the first to be discovered. It is also an extremely important and easily deficient fat-soluble vitamin necessary for the body to maintain normal metabolism and function. It was developed by American scientists Elmer Mc Collum and MaggAret DAvis in 1912-1914. Found between. In fact, as early as 1,000 years ago, Chinese medical doctors in the Tang Dynasty

Vitamin A refers to all compounds that have the biological activity of retinol. There are two broad classes of substances that provide retinol bioactivity. One is retinol, its metabolites, and synthetic analogues with similar structures. This class is also known as retinoids, also known as preformed vitamin A. The main dietary source is animal origin. Retinol and retinyl esters in food. Another type of substance is vitamin A pro-carotenoids, which are carotenoids derived from plant foods that can be converted into retinol in the body. They are precursors of dietary retinol, mainly including -carotene. , Alpha-carotene and beta-cryptoxanthin. ^[4]

The common methods for detecting vitamin A are:

Vitamin A has a wide range of important physiological functions in the human body. In summary, it mainly includes vision, cell proliferation and differentiation regulation, information exchange between cells, and immune response. The lack of vitamin A can cause abnormal physiological functions and pathological changes. ^[4]

Vitamin A is mainly used for the prevention and treatment of night blindness and dry eye, and also for local purulent infection of the skin after burns. Vitamin A for humans should not exceed 3 mg / day for adults and 2 mg / day for children. If you take a large dose of vitamin A, acute vitamin A will occur because the excretion ratio is not high. The main symptoms are short-term hydrocephalus and vomiting, and some may have symptoms such as headache, drowsiness and nausea [9]. Toddlers who take large doses of vitamin A for a long period of time will experience symptoms of excessive vitamin A, which are mainly hepato-splenomegaly, decreased red blood cells and white blood cells, excessive bone marrow growth, brittle long bones, and prone to fractures. A new Swedish study shows that middle-aged men with high levels of vitamin A in their blood have a much higher chance of fractures during their old age than those with low levels of vitamin A in their blood. Therefore, for the human body, vitamin A is indispensable and cannot be abused. As long as the diet is rich in vitamin A or carotene, it can effectively prevent vitamin A deficiency without taking additional vitamin A supplements. ^[3]

The toxic and side effects of vitamin A mainly depend on the intake of retinol and retinyl esters, and are related to the physiological and nutritional status of the body. Liver vitamin A concentrations exceeding 300 mg / g are considered to be excessive and cause clinical manifestations of toxicity. The clinical manifestations of acute vitamin A overdose include severe rash, headache, and pseudo brain tumor coma leading to rapid death. Chronic overdose is relatively common and clinical manifestations include symptoms of central nervous system disorders, liver fibrosis, ascites, and skin damage. Recently there have been reports of myelosuppression caused by excessive vitamin A in infants, and hypercalcemia caused by chronic excessive vitamin A in adults. Studies have found that oil-based vitamin A or liver-derived vitamin A is only 1/10 as toxic as hydrated, emulsified, and solid retinol supplements. ^[4]

Vitamin A deficiency has clinical and functional characteristics. For individuals with primary vitamin A deficiency, tolerance varies from person to person, depending on a range of geographic and epidemiological factors. The clinical manifestations of vitamin A deficiency are mainly symptoms and signs of eye and vision and other epithelial dysfunction. ^[4]

Vitamin A deficiency is the main cause of blindness in children in developing countries, and it is also a common nutritional deficiency in children in developing countries. Because of the effects of VAD (Vitamin A Deficiency) and SVAD (Vitamin A Marginal Deficiency) on children's health, the prevention and control of VAD and SVAD has become one of the public health issues that need to be addressed worldwide. ^[5]

The WHO and UNICEF conduct vitamin A interventions in a variety of ways, including increasing consumption of vitamin A-containing foods, fortifying vitamin A with food, increasing breastfeeding, and regular high-dose vitamin A supplementation. ^[5]

A Vitamin A vitamin A nutritional status assessment

Accurately assessing the vitamin A nutrition level of susceptible individuals and populations is of great significance for the study of the formulation, implementation and evaluation of VAD, SVAD and nutrition intervention strategies. The commonly used methods to check the vitamin A nutritional status of groups or individuals in actual work mainly include: clinical examination of dry eye disease, diet survey, determination of dark adaptation ability, inquiry of night blindness history, determination of serum retinol content, relative dose response test , Isotope dilution method, determination of liver vitamin A content and conjunctival blotting cell method. ^[5]

Vitamin A nutrition education and reasonable dietary measures

Dietary interventions to increase the intake of vitamin A-rich foods in the region through nutrition education and reasonable dieting have long been considered the most important

Balanced nutrition

It is a lasting method that can fundamentally improve the condition of VAD and SVAD. Nutrition education should focus on promoting breastfeeding and increasing the supply of milk, eggs and dark vegetables. ^[5]

A Vitamin A food fortified with vitamin A

Vitamin A and retinol equivalents in food

Food fortified vitamin A is a direct, effective, and inexpensive method for preventing and treating VAD and SVAD. The general concept of food fortification of the Chinese National Public Nutrition Project Group identified vitamin A, vitamin B1, vitamin B2, folic acid, nicotinic acid, iron, iodine, zinc, and calcium as the main nutrients for nutrient fortification in China. ^[5]

A Vitamin A supplements regularly with vitamin A preparations

Regular vitamin A supplementation is a quick and direct way to improve vitamin A nutritional status. It includes clinical supplements for children with clinical dry eye disease, measles, and malnutrition, targeted delivery using existing health service coverage, and preventive supplements for all high-risk groups. ^[5]

At present, the WHO's prevention and treatment of vitamin A deficiency in different high-risk groups needs to make the following suggestions ^[5] :

Infants under 5 months (including newborns): Vitamin A supplementation is not recommended. The effect of vitamin A supplementation on reducing infant morbidity and mortality remains to be further confirmed by future randomized controlled trials. The relationship with immune function and determination of appropriate evaluation indexes of VAD in this age group are further studied. ^[5]

Children between 6 and 59 months: It is recommended to promote high-dose vitamin A supplementation for children aged 6 to 59 months when VAD is a public health problem (that is, the incidence of VAD in this population is 20% or the incidence of night blindness is 1%). Infants at 11 months (HIV + or-) are supplemented with 100,000 IU, and infants between 12 and 59 months are supplemented with 200,000 IU every 4 to 6 months. In the future, further research on better vitamin A supplementation methods is needed to improve the understanding of the co-intervention effect of vitamin A and vaccines in order to seek better clinical and biochemical VAD evaluation indicators.

Pregnant women: Vitamin A supplementation is not recommended as part of routine antenatal care to prevent the onset and death of pregnant women and infants, and VAD is a serious public health problem (ie, the incidence of night blindness in pregnant women or infants between 24 and 59 months is 1%) Pregnant women in regions or countries (pregnant women) can supplement with vitamin A to prevent night blindness. The supplementary dose: 10,000 IU for pregnant women over 12 pregnant women or 25,000 IU per week, but the duration and frequency of supplementation need further research. . More research in the future should focus on a comprehensive review of vitamin A supplementation during pregnancy, especially the impact of other interventions on mortality and the impact of vitamin A supplementation on breast milk vitamin A levels during the third trimester of pregnancy.

Nursing mothers: Vitamin A supplementation is not recommended as an intervention to prevent morbidity and death of mothers and infants. The effects of supplementing 200,000 IU of vitamin A on breast milk's retinol levels in breast milk and its metabolism, dose distribution, and excretion at 6 weeks postpartum remain to be further studied.

Maternal and child HIV infection: Vitamin A supplementation is not recommended for HIV-positive mothers. ^[5]