Text | "China Science News" reporter Yan Tao
Coffee is a "life-sustaining artifact" for many people, and it depends on it to refresh the mind and relieve fatigue. If you don't have time to sit in a coffee shop and savor it slowly, some people will also choose to make a cup of instant coffee at hand, which is simple and quick.
In March 2023, an article on coffee by the team of Associate Professor Shen Mingwang and Professor Zhang Lei of Xi'an Jiaotong University was published in Nutrients, an international journal in the field of nutrition.
But to the team's concern, this conclusion was misinterpreted by some media outlets as "telomere length decreases by 0.38 years with age for every additional cup of instant coffee consumed." And derived the fallacy that "drinking instant coffee will reduce human lifespan", and the "life-sustaining artifact" became a "life-urging killer" overnight. So, what is the actual conclusion? Does instant coffee have a direct impact on human life? Recently, Shen Mingwang's team was interviewed by China Science Daily to interpret their research results.
The human body does have an "hourglass of life"
Previous studies have shown that regular coffee consumption is beneficial to the human body. Coffee stimulates the body's central nervous system, promotes the release of neurotransmitters, and increases the activity of neurons. Many people drink black coffee can also improve the body's metabolism and circulation, resulting in fat loss and weight loss.
Since coffee is mostly beneficial and harmless, why is it only instant coffee that is "branded as a villain"?
In human DNA there is a non-coding repeat called a telomere, which together with histones forms a small DNA-protein complex. Telomeres themselves are non-coding DNA and are not responsible for the synthesis of any proteins, but they play a much more important role. It is located at the end of the chromosome, similar to wearing a very high "hard hat" on the chromosome, which plays a role in maintaining the stability of the DNA and avoiding damage to the genome.
The discovery of telomeres and telomerase to protect chromosomes won the Nobel Prize in Physiology or Medicine in 2009.
As we all know, all cells of the human body are always in the process of dividing, or on the road of preparing to divide. 50-100 DNA base pair sequences are lost with each cell division.
Telomeres work to protect the integrity of chromosomes during cell division while controlling the cycle of cell division by monitoring the degree of chromosome integrity. The length of the telomeres is also reduced during this process, which requires that the telomere length should not be too short. When telomeres are worn out and shortened to a certain extent during cell division, the cell stops dividing and telomeres "heroically take justice" with the important chromosomes and genetic information they protect.
Therefore, telomere length can also be considered as one of the indicators of biological aging, and some studies in the past have linked shorter telomere length to several aging-related diseases. Some people refer to telomeres as "life timers", and some people even compare telomeres to life-saving hourglasses, which have been leaking since birth, and when the sand inside runs out, life is over.
Telomeres are akin to wearing a tall "hard hat" on a chromosome.
How is coffee related to telomeres?
Shen Mingwang told reporters that as the core backbone of the "Shaanxi Provincial Key Laboratory of Disease Prevention and Control and Health Promotion Research" and the "Sino-Australian Joint Research Center for Infectious Diseases" of the School of Public Health of Xi'an Jiaotong University, the team has been carrying out multidisciplinary integration in research, and the previous results have combined mathematics, statistics, economics, management, clinical medicine and public health and other multidisciplinary content. At present, this study is mainly from a statistical point of view, using the existing database, to analyze the relationship between different coffee and human DNA telomeres.
"In this study, we did not explore the mechanism of action of coffee from a micro perspective, but conducted statistical analysis based on population data. According to the classification of coffee in the relevant database, we divide coffee into instant coffee and filter coffee, which is also the most common type of coffee in our lives. The first author, Dr. Wei Yudong, told China Science News.
Wei Yudong said that the specific ingredients in instant coffee were not the content of their team's research, and the team mainly explored the causal relationship between coffee intake and telomere length through some statistical methods, such as multiple linear regression for correlation judgment and Mendelian stochastic method for causality judgment.
Study Participant Flow Chart. (All photos provided by the research group)
It is understood that the team analyzed 468924 participants in the UK Biobank database, aged between 37-73 years, and collected the participants' coffee intake through a dietary questionnaire. According to different types of coffee, the team of researchers divided coffee intake into three types: coffee intake, instant coffee intake and filtered coffee intake. Statistically, among all participants, 55.6% were younger than 60 years old, 54.2% were women, 50.5% drank more than one cup of coffee per day, and in the questionnaire, 69.1% and 55.3% drank more than one cup of instant or filtered coffee per day.
The team obtained the raw telomere length data from the database, and then performed multiple linear regression between the raw telomere length data and coffee intake to obtain a key coefficient of 0.38.
0.38 years: the length of life shortened?
How did this "0.38 years" come about? Is it equal to the time of actual life expectancy? Wei Yudong denied this statement.
Wei Yudong explained that the team first analyzed the relationship between daily instant coffee intake (which is a grade variable, including 0 cups, < 1 cup, 1 cup, 2 cups, 3~5 cups, >6 cups) and telomere length (the unit is often expressed by the T/S ratio, representing the ratio of telomere length (T) to the length of a single copy gene (S)) through multiple linear regression, and obtained the coefficient "β=-0.0088". "The coefficient of 0.0088 is statistically significant, and the average daily consumption of 1 cup of instant coffee shortens the telomere by 0.0088 unit length. Wei Yudong said.
When you see this number, you may not understand what it means. βReferring to the previous Lancet Healthy Longevity approach, the team combined the change in telomere length with the change in longevity by 0.023 (i.e., 0.023 unit lengths of telomeres for every 1 year of growth) to transform the coefficient β obtained by their team. After conversion (0.0088/0.023=0.38), the final number "0.38 years" was obtained (the effect of drinking an extra cup of instant coffee per day on telomere length is equivalent to the effect of aging on telomere length by 0.38 years).
However, it is worth noting that 0.023 is the value of the relationship between telomere length and lifespan obtained by the researchers by adjusting for multiple confounding factors, and in reality, telomere length and lifespan are affected by many factors.
At the same time, the results of the study are only the relationship between instant coffee and telomere length, which is converted to 0.38 years for ease of understanding. It can be thought that 0.38 years is only a conversion of values and units, and not a direct relationship between instant coffee and lifespan. "There is a direct relationship between instant coffee and longevity, and we didn't do a study. Even though we refer to the previous literature, this is only a correlation and does not illustrate a direct causal relationship between instant coffee and longevity. Wei Yudong further explained.
"0.38 years is an indirect conversion relationship, and it cannot be simply understood as equivalent to a reduction in life span of 0.38 years. Shen Mingwang also told reporters, "At the same time, this study uses a 24-hour dietary review questionnaire, that is, the daily average dietary intake is calculated by the participants answering the questionnaire many times." Therefore, the study reported that 'one more drink per day' should be understood as 'an increase in one cup to the average daily intake'. ”
According to Shen Mingwang, the relationship between telomere length and lifespan is not so simple and will be affected by many factors. Even when the team studied the relationship between instant coffee and telomere length, it was based on the possibility of a large number of persistent typical samples, and there was no need to panic about instant coffee because of this number.
After the team's results were published last year, there were some false reports from the media, intercepting part of the results, claiming that "every cup of instant coffee will shorten the lifespan", and even some relatives and friends around came to consult the team whether drinking instant coffee will accelerate aging or affect lifespan.
Shen Mingwang told China Science Daily that the length of telomeres is shortened by a certain value, and the corresponding human life expectancy will age or shorten how much time, which is another research topic involving conversion, and it is difficult to draw this conclusion from current research. And the database used by the team is from the United Kingdom, which is different from the genetics and eating habits of Chinese. Therefore, based on the current research, no direct causal relationship between coffee and longevity can be derived.
Why does drinking instant coffee shorten telomeres, and what is the mechanism of this? Shen Mingwang guessed that it may be related to some ingredients in instant coffee, especially various additives such as creamer and flavoring. But this is only speculation, and more research is needed to confirm it.