Can air purifiers improve health?

air pollution beijing china

What is the most popular New Year gift in China this year? In addition to the new year and red envelopes, you may also be able to send an "inexhaustible gift": indoor air purifier. Undoubtedly, since last year, they have become popular in China and their sales have been blown out. I think this is a good change: including myself, many independent tests have shown that a good air purifier can greatly improve indoor air quality, reduce PM2.5 content by 80% or more, such as I am at home In the bedroom and living room, I have tested multiple brands of purifiers. But is there reliable data to prove that it does make you healthier? Of course, reducing exposure to pollution can reduce the effects of harmful health, which seems to make sense. But in the history of medicine, no shortage of common sense and traditions have later proved to be ineffective or harmful – such as bloodletting, or more modern traditions of taking multivitamins. Readers of this article, a large group of people taking multivitamins every day, think that this is "healthy", but there is strong evidence that they have no effect and may even be harmful to people. Is an air purifier an example of this?
In terms of theory and testing, a good air purifier should improve indoor pollution levels by more than 80%; this 80% boundary is also the AHAM's clean air delivery rate (Clean Air Delivery) Rate, referred to as CADR) The boundaries used in the tests, which are widely cited in the air purifier comparison chart. So, suppose you have installed a top purifier in your living room, you feel satisfied and safe, but how long can you stay in this room? Or is it possible that the purifier is too small and the room is too large, the purifier is too old, the fan speed is too slow, or is the window open? Has your original asthma and cardiovascular disease improved after installing the purifier? Understand what I mean? I want to take this topic to the next level and look for evidence that your health has improved when using these devices. I hope to be able to tell my patients and readers that in the published research, there is indeed a study that tracks the subjects for months or even years, and they and the control group (people who do not use air purifiers) For comparison, assess their health and see if there is improvement in heart disease and lung disease, cancer and mortality. Is there such a study?

In search of the best research, I searched the Pubmed scientific database and found no strong data. Although I was disappointed, I was also surprised. A well-designed research project like this is difficult and costly to implement. But there are still a few attempts, especially for the use of high-efficiency particulate air filters (HEPA) to help children with asthma. One of them was a systematic study published in 2002. The results showed that the filter was effective but not effective in improving asthma symptoms, and the differences between the different studies were large, which increased the difficulty of summative evaluation. A more recent, well-designed study was published in the 2011 Pediatrics, which tracks 200 asthmatic children exposed to second-hand smoke in the home environment, and has half of the children's bedrooms equipped with real HEPA. The purifier, the other half got the comfort purifier, the shape is the same as the ordinary purifier, but no effective filtering device such as HEPA or activated carbon is installed. A year later, the number of children who used HEPA to see an asthma clinic decreased, which may – but not be determined – was due to a 25% reduction in PM2.5 in their room.

Other studies focus on allergies, including an interesting study in 2008. The study evaluated children with a history of allergies to animals, followed them for one year, and recorded their lung function and blood markers. One year later, there was no significant difference in lung function, anti-allergic drug use, or blood markers for HEPA air filter users, but there was a trend toward improved bronchial hyperresponsiveness in children. Another study in 1990 was even more impressive, showing that not only did indoor PM0.3 decreased by 70%, but the patient's allergy symptoms improved.

All of this suggests the health benefits of air purifiers, but for us in China and the developing world, these studies are still on the verge of the answer I want to know. In the United States, the marketing and testing of most air purifiers focus on allergies and asthma. But in developing countries, air pollution is more severe, so health risks are much more serious. We are concerned about the long-term risks of pollution to death, heart disease, lung disease and cancer. The studies I just mentioned still can't answer the more in-depth question: Can long-term use of indoor air purifiers prevent premature death, heart disease, lung disease and cancer?

The best research I have found was released in January 2013, "Indoor Air." This complex research design is very meticulous. In a random double-blind crossover design, 20 households participated, using an air purifier or a comfort purifier for more than three weeks. The family tested was in the distant First Nations community, and the main purpose was to assess whether the air purifier could improve heart and lung health. As their summary says:

“...Every household receives an electrostatic air purifier and a comfort purifier, used for one week, in random order. At the beginning and end of each week, their lung function, blood pressure and endothelial function are measured... on average Calculated, the person using the air purifier increased the forced expiratory volume by 217 ml in one second, the systolic blood pressure by 7.9 mm Hg, and the diastolic blood pressure by 4.5 mm Hg. We observed the indoor PM2.5 and Consistent reverse correlation between lung function. Overall, our findings suggest that reducing indoor PM2.5 in First Nations communities may lead to improved lung function."

The Canadian research team also previously published a similar study that tested 45 non-smokers in 20 households using a wood-fired fireplace for 7 days, comparing the health status of the subjects with or without the HEPA purifier. The endothelial function of the purifier user and the performance of inflammatory biomarkers such as C-reactive protein (CRP) have improved. Since most polluting researchers now view pollution as an inflammatory disease, the test results of such biomarkers can indeed be an accurate indicator of future health problems. This method was also used in the air pollution mask study I recently reviewed.

How do I understand these studies? First, they all affirm the information we already know: air purifiers can reduce indoor PM2.5 levels, but the results are uneven. The second is the result of looking at the health markers. I think the most encouraging finding is that even in such a short period of time (less than a month), the study of the First Nations showed an improvement in lung function. Although blood pressure improvement data is not convincing enough, a broader study may help confirm the positive conclusions they initially made.

I don't think these studies are worthy of the evidence on the board, but I really don't know if we will have more well-designed surveys like these studies in the future, because such research requires a lot of money and a large number of people, so it must be high. The amount of the project fund can be carried out. But before a better research release, we must rely on what is currently known:

· In terms of PM2.5, there is no so-called “safety” level of air pollution, which is always as low as possible.

· Deteriorating air pollution can cause death from a variety of causes, especially heart and lung diseases and cancer. Many studies have shown this, including the 2013 China Demographic Analysis.

· On the positive side, long-term improvements in PM2.5 do help reduce mortality. The best study to prove this is an ambitious epidemiological analysis of all urban populations in the United States, spanning from the 1970s to the 1990s, during which air quality in the United States generally improved. There are many reasons why people's average life expectancy has been extended, but it is estimated that 15% of the extended life comes from clean air.

· Short-term studies have also shown that reducing outdoor air pollution can help improve health. The best research I have ever seen in this area occurred in Beijing during the 2008 Olympics. A group of researchers tracked 125 healthy young doctors, tracking time before, during and after the Olympics, and found that blood pressure, heart rate and other inflammatory biomarkers were observed during the good days of air pollution improvement. Both have improved. Another encouraging study tracked pregnant women and their babies in Tongliang County, Chongqing. Studies have shown that after a local coal-fired power plant was forced to close in 2004, the results showed that the 2-year-old children had higher levels of health and muscle coordination than the control group (children born before the power plant was shut down).

Are all these enough to convince you to use an indoor purifier? For me, I have believed it a few years ago – not only because of common sense, but also because of biochemistry, it does make sense, and it also fully complies with the precautionary principle: “When an activity has an environmental or human health The threat of injury should be precautionary, even if some causality has not been fully confirmed scientifically."

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