May Science Gossip List： Wind and rain accelerate the spread of Covid-19？ fake

　　Wind and rain will accelerate the spread of Covid-19, high temperature in hot summer can end the virus, blood donation for the elderly can reduce blood lipids, and China is the only big country with compulsory iodization of salt … … These hottest topics you have heard recently are actually "false propositions". In May, the "Science" gossip list was released, which involved five popular health rumors. Let’s see if you have been fooled. "Every month ‘ Science ’ The "Gossip List" is directed by Beijing Science and Technology Association, Beijing Internet Information Office and Capital Internet Association, and jointly released by Beijing Science and Technology Journalists Editors Association and Beijing regional websites.

　　Myth: The wind will blow the virus everywhere, and the rain will make the virus multiply faster, which will accelerate the spread of Covid-19.

　　Truth: nonsense. First of all, the gale will not only accelerate the spread of Covid-19, but also slow it down.

　　Strong winds do blow viruses everywhere, but they don’t blow them all to the same place, only high-concentration viruses are blown away. In an interview with the media a few days ago, Academician Zhong Nanshan said that the virus has to attach to something to spread, the most prominent thing is to spread it through droplets. The virus will soon be diluted in the strong wind, and the virus will naturally not spread unless it reaches a certain concentration in the air.

　　Besides, the rain will not increase the spread risk of Covid-19. In a humid environment, bacteria may reproduce faster, but viruses, unlike bacteria, can only be parasitic in the host to reproduce, so humidity will not increase the number of viruses. In addition, the virus floats in the air in the form of tiny droplets. After the rain, these tiny droplets will attach to the rain and fall to the ground and be washed away, so that they cannot enter everyone’s nose and mouth and cause infection. In other words, rain will not only accelerate the spread of Covid-19, but also reduce the number of viruses floating in the air and reduce the risk of infection.

　　Myth: Covid-19 is afraid of heat. As the temperature rises in summer, the spread of Covid-19 will end.

　　Truth: As the weather starts to get hot, wearing a mask becomes more uncomfortable, but this is no reason not to wear a mask and relax your vigilance. Hot weather can indeed reduce the spread of COVID-19, but the effect is limited.

　　Christopher Murray, director of the Institute of Health Indicators Evaluation at the University of Washington, said that through statistical research, they found that for every 1℃ increase in temperature, the transmission rate of Covid-19 would be reduced by about 2%. But it is impossible to successfully contain the virus by high temperature alone. For example, Australia, a southern hemisphere country in summer, and Singapore and Malaysia, which are located in the tropics and have high temperature and rain all the year round, the epidemic situation is still serious.

　　Public preventive measures such as isolation, keeping social distance and wearing masks are more effective than simple temperature. Don’t be lucky just because the weather is sultry, and don’t wear a mask at will.

　　Myth: Old people often donate blood, which can lower blood fat.

　　Truth: According to the guidance of relevant professional organizations, proper blood donation will not be harmful to health. But blood donation can’t be used as a means to reduce blood fat.

　　The total blood volume of a healthy person accounts for about 8% of the body weight, which is about 4000-5000 ml. Usually, 80% of the blood circulates in the heart and blood vessels, maintaining normal physiological functions; 20% of the blood is stored in the liver, spleen and other organs. When blood loss or strenuous exercise occurs, the blood will enter the blood circulation system. A person donates 200-400 ml of blood at a time, accounting for only about 5% of the total blood volume. The stored blood will be replenished immediately after blood donation, so blood donation will not reduce the circulating blood volume, nor will it affect people’s health function.

　　Theoretically speaking, blood donation has removed some blood, and the blood lipid may decrease slightly in the short term. But in fact, our body has the ability of self-regulation. When the blood lipid content drops, the body will produce blood lipid quickly, so even if the blood lipid drops slightly in the short term after blood donation, it will soon be adjusted back to the original level.

　　Therefore, blood donation as a means to reduce blood lipids is not worth advocating. In fact, the simplest and most effective way to reduce blood lipid is to take blood lipid-lowering drugs according to the doctor’s advice, besides healthy diet and reasonable exercise.

　　In addition, China’s "Blood Donation Law" stipulates that citizens who are 18-55 years old, men weigh more than 50 kilograms, and women weigh more than 45 kilograms can participate in blood donation. Due to reasons such as diet or nutrient absorption, the elderly are not encouraged to donate blood.

　　Myth: China is the only big country where iodized salt is compulsory, while iodized salt is rarely used abroad.

　　Truth: Iodine deficiency is a global public health problem, and iodine fortification through food is the fundamental way to solve this problem. Since 1993, the United Nations and the World Health Organization have carried out comprehensive iodization of salt around the world, that is, edible salt for human consumption, salt for animal feed and salt for food industry are all iodized. By 2008, more than 120 countries and regions around the world have implemented the policy of strengthening salt iodine, among which 34 countries and regions have implemented compulsory iodization of salt, including China and India, which have the most population. From 1993 to 2013, the number of iodine-deficient countries and regions decreased from 110 to 31.

　　"There is little iodized salt abroad" and "there is no compulsory iodization abroad" are just appearances. This is because different countries have different dietary structures and different salt habits, and have adopted different iodine fortification strategies. For example, in Thailand and Cambodia, because the most commonly used salty seasoning is not salt but fish sauce, iodine is added to fish sauce, so there is no iodized salt; About 75% of the salt intake of consumers in western countries comes from processed foods, so it is a popular practice for them to strengthen iodine in processed foods, especially bread.

　　Iodine fortification policies vary widely in different countries, but the ultimate goal is the same: to achieve adequate iodine nutrition for all. China people’s eating habits determine that salt iodization is the most extensive, effective and economical iodine fortification strategy in the retail sector.

　　Myth: It doesn’t matter if children are fat when they are young, they will naturally lose weight when they grow up.

　　Truth: In the past decades, the global prevalence of overweight and obesity among children has been increasing year by year. In childhood, obesity is not only closely related to asthma, adenoidal hypertrophy, childhood diabetes, childhood fatty liver, central precocious puberty and other diseases, but also may affect the health of adults.

　　According to the research of China CDC, during the 13-year follow-up, 80% of obese children will develop into adult obesity. Therefore, it is an important problem for public health and clinicians to prevent the growth of childhood obesity.

　　In fact, bad eating habits are closely related to childhood obesity, such as skipping breakfast, frequent intake of snacks and sugary drinks, and eating too fast. School-age children should pay attention to the relatively fixed time of three meals, balanced nutrition and less oil and salt seasoning; Drink plenty of water, do not drink sugary drinks, and drink more boiled water; Do not overeat, because overeating may increase the burden on children’s digestive system, cause heat accumulation, and lead to overweight and obesity in children.

　　How to judge whether a child is overweight or obese? A simple assessment can be made by children’s BMI. Body mass index (BMI), referred to as body mass index. BMI calculation formula: BMI = weight (Kg)/square of height (m2). For example, if a 52Kg person is 1.55m in height, the BMI is: 52 (kg)/square of 1.55 (m2)= 21.6. At the same time, it was evaluated according to the Growth Curve of Body Mass Index of Children and Adolescents aged 0-18 in China. If the child belongs to the category of overweight and obesity, it is necessary to go to the hospital as soon as possible to evaluate whether there are other obesity complications, and at the same time formulate effective diet and exercise strategies to prevent the further development of obesity.

　　Text/reporter Li Jie