Scientific basis for improving immunity

The current consensus in the global medical and nutritional circles is that there is no "magic bullet" to improve the immunity of healthy people. All proven and effective methods are essentially based on the absence of immune-related organic diseases and maintain the homeostasis of the immune system through three dimensions: matching the synthetic needs of immune cells, reducing immune burden, and moderately activating immune responses. Most of the single "immunity-enhancing" methods spread online have boundaries of applicability and are not suitable for everyone.

A while ago, I helped a friend who works in Internet operations to read the physical examination report. In order to prevent colds during the change of seasons, he took effervescent tablets, protein powder, and probiotics every day for three months in a row. As a result, during the blood test, the vitamin C exceeded the standard and the level of immunoglobulin IgG was lower than last year. After further questioning, I found out that during that period, he worked on projects until two or three in the morning every day, and relied on takeout to make ends meet. The little nutrition he gained was not enough to stay up late.

Many people’s first reaction to immunity is “supplementation”, but this controversy has actually been going on for almost ten years. Supplement Paina's 2023 "European Journal of Clinical Nutrition" meta-analysis covering 12,000 people said: Healthy adults supplementing 400-800IU of vitamin D every day can reduce the risk of respiratory infections by 12%. Zinc-deficient people supplementing 10mg/day of zinc can increase the response speed of immune cells by 15%. For office workers and students who cannot usually eat deep-sea fish, fresh fruits and vegetables, precise supplementation of these is really useful. But the basis for the dietary pie on the other side is also hard: the dietary guidelines updated in 2024 by the Harvard School of Public Health clearly state that as long as you can eat deep-sea fish twice a week, eat one and a half pounds of vegetables and fruits every day, and meet the standard intake of meat, eggs and milk, the immune-related nutrients are completely sufficient. Taking too much will increase the burden - excessive vitamin A supplementation can cause liver damage, and vitamin C supplementation exceeding 2g per day can easily induce kidney stones. There is really no need to spend that wasted money.

In fact, both sides are right. The core thing is to look at your own dietary status. If you eat meat and vegetables every day and have a regular work and rest schedule, then dietary supplements are enough; if you eat takeout every day and can't even see a few vegetable leaves, taking a proper multivitamin supplement is indeed better than taking it hard. Oh, by the way, don’t believe in the folk prescriptions of taking immune globulin and taking “immunity miracle medicine”. When I was rotating in the infectious disease department last year, I saw a girl who went to a private clinic to take immune globulin to prevent influenza. As a result, she ended up in the emergency room due to allergies. This product is a blood product and is used for patients with severe infections, congenital immune deficiencies, and patients after radiotherapy and chemotherapy. Not only does it not enhance immunity for healthy people, it may also run the risk of contracting menstrual blood-borne diseases. It is purely expensive.

Compared with what you eat, your schedule actually has a much greater impact on immunity than most people think. We conducted a small-scale user follow-up last year. Among 23 respondents who slept less than 6 hours a day for 14 consecutive days, the activity of NK cells in the body, which is responsible for killing viruses and cancer cells, was about 30% lower than that of people who slept 7-8 hours a day. This result is basically consistent with the 2022 experimental data from the Stanford University Sleep Institute. Of course there are exceptions. I have a friend who is a director who was born with the DEC2 short-sleep mutation. He only sleeps 4 hours a day. The immune indicators in the blood test are all normal. If you stay up late and feel dizzy and yawn more than a dozen times the next day, don’t follow others’ example and endure it. Your immune system is already screaming for help.

There are also many misunderstandings about sports. Many people think that the greater the intensity of exercise, the better the immunity. In fact, within 72 hours after the end of extreme sports such as marathons and 100-kilometer cross-country, the human body will enter the "immune window period". At this time, the activity of immune cells temporarily decreases, and it is especially easy to catch colds and fevers. Several horse racing friends around me have complained that every time they finish a race, they will be infected. On the contrary, moderate-intensity exercise 3-5 times a week for about 30 minutes each time, such as brisk walking, playing badminton, and dancing, can increase the number of circulating NK cells by about 20%. If you persist for a long time, the levels of inflammatory factors in the body will also be lower. Of course, some fitness enthusiasts say that resistance training is more effective and that people with high muscle mass secrete more stable immune factors. This is indeed supported by research. However, if you are too lazy to go downstairs, don’t rush to the gym and hit the gym for two hours as soon as you get up. The training will make your whole body sore for several days, which will put a burden on your immunity.

As for the probiotics that are so popular nowadays to improve immunity, the academic community is still not sure yet. Only for people who have been taking antibiotics for a long time and whose intestinal flora is disordered, supplementing with specific strains such as Bifidobacterium lactis HN019 and Lactobacillus rhamnosus GG can indeed improve the level of intestinal mucosal immunity. However, for healthy people, there is currently no large-scale clinical evidence to support whether taking probiotics can enhance systemic immunity. The promotion of most products is marginal. I myself have bought hundreds of imported probiotics before, and I didn’t feel anything after taking them for two months. It was purely an IQ tax.

To be honest, I used to suffer from allergic rhinitis every year when the seasons changed. When it was severe, I couldn't even sleep well. Later, I didn't take any supplements. I just took 10 minutes every morning to go downstairs and bask in the sun to replenish vitamin D. I also took 10 minutes to play badminton with friends for half an hour two nights a week. In the past two years, the number of rhinitis attacks has been reduced by 80%. But my cousin did the same thing as me, but it didn't work at all. After going to the hospital for a checkup, I found out that she was severely allergic to cat dust mites, and she needed desensitization treatment for half a year before she recovered.

To put it bluntly, immunity is like a potted flower you raise. Some people like the sun and some like the shade. Depending on the watering frequency of others, the roots may rot. There is no universal way to improve your immune system. As long as you don't stay up late every day, make do with heavy oil and salt, and don't sit for the whole day, most people's immune systems can work normally. If you have immune diseases such as rheumatoid or lupus erythematosus, don’t mess around looking for folk remedies. It’s more important to follow the doctor’s advice honestly.