Coffee, for many, is a lifesaver - it perks you up, wards off fatigue, and keeps you going. When there's no time to savor a cup at a café, some opt for the quick fix of instant coffee, convenient and easy.
In March 2023, Associate Professor Shen Mingwang and Professor Zhang Lei from Xi'an Jiaotong University published an article in the renowned international journal Nutrients, shedding light on the association between instant coffee consumption and the shortening of DNA telomeres in the human body.
However, the team was troubled when some media outlets misinterpreted their findings, suggesting that "for each additional cup of instant coffee consumed, telomere length decreases by 0.38 years with age," spawning the fallacy that "drinking instant coffee reduces human lifespan." Overnight, the "lifesaver" turned into a "life-shortening villain." So, what's the actual conclusion? Does instant coffee directly impact human lifespan? Recently, the team led by Shen Mingwang clarified their research findings in an interview with the Chinese Science Bulletin.
Indeed, the Human Body Has a "Lifespan Hourglass"
Previous studies have shown that regular coffee consumption is beneficial to the human body. Coffee stimulates the central nervous system, promotes neurotransmitter release, and increases neuronal activity. Many people even find that drinking black coffee enhances metabolism and circulation, aiding in weight loss efforts.
Instant coffee versus filtered coffee.
Since coffee is mostly harmless, why is instant coffee often portrayed as the villain? It all comes down to the DNA.
Within human DNA lies a region of non-coding repetitive sequences called "telomeres," which, along with histones, form a small DNA-protein complex. While telomeres themselves do not encode any proteins, they play a crucial role. Situated at the ends of chromosomes, they act like high-security "caps," maintaining DNA stability and preventing genomic damage.
The discovery of telomeres and telomerase, enzymes that maintain chromosome ends, earned the 2009 Nobel Prize in Physiology or Medicine.
It's well-known that cells in the human body are constantly dividing or gearing up for division. Each cell division results in the loss of 50-100 DNA base pairs.
Telomeres safeguard chromosome integrity during cell division and regulate the cell cycle by monitoring chromosome completeness. As cells divide, telomeres shorten, and when they reach a critical length, cell division halts, sacrificing themselves along with the genetic information they protect.
Hence, telomere length serves as a marker of biological aging, with previous studies linking shorter telomeres to several age-related diseases. Telomeres are often referred to as "biological clocks" or likened to hourglasses of life, where the sand starts flowing from birth, and when it runs out, life concludes.
Telomeres are like high "safety hats" worn by chromosomes.
But what's the deal with coffee and telomeres?
Shen Mingwang told reporters that as a core member of the "Key Laboratory of Disease Control and Health Promotion Research in Shaanxi Province" and the "Sino-Australian Joint Research Center for Infectious Diseases" at the School of Public Health, Xi'an Jiaotong University, the team has been conducting interdisciplinary fusion in research, combining mathematics, statistics, economics, management, clinical medicine, and public health. Previous achievements have integrated various disciplines. Currently, the team's research mainly starts from a statistical perspective, utilizing existing databases to analyze the relationship between different types of coffee and human DNA telomeres.
"In this study, we did not explore the mechanism of coffee from a microscopic perspective, but conducted statistical analysis based on population data. According to the classification of coffee in the relevant database, we divided coffee into instant coffee and filtered coffee, which are the most common types of coffee in our daily life," said Dr. Wei Yudong, the first author of the study, to the "Chinese Science News."
Wei Yudong said that the specific components of instant coffee were not the focus of their team's research. The team mainly used statistical methods, such as multiple linear regression for judging correlation and Mendelian randomization for judging causality, to explore the causal relationship between coffee intake and telomere length.
Research Participant Flowchart
The team analyzed data from 468,924 participants in the UK Biobank database, aged between 37 and 73. Participants' coffee intake was collected via dietary questionnaires, categorized into three types: total coffee intake, instant coffee intake, and filtered coffee intake. Statistical analysis revealed that among all participants, 55.6% were under 60 years old, 54.2% were female, and 50.5% consumed more than one cup of coffee per day. Additionally, 69.1% and 55.3% reported consuming more than one cup of instant or filtered coffee per day, respectively.
The team obtained raw telomere length data from the database and conducted a multiple linear regression, resulting in a crucial coefficient of 0.38.
But what does "0.38 years" mean in terms of shortened lifespan? Is it equivalent to the actual reduction in lifespan? Wei Yudong refuted this notion.
Explaining further, Wei Yudong stated that the team initially analyzed the relationship between daily instant coffee intake (as a categorical variable, including 0 cups, <1 cup, 1 cup, 2 cups, 3-5 cups, >6 cups) and telomere length (expressed in the commonly used T/S ratio, representing the ratio of telomere length (T) to single-copy gene (S) length). The obtained coefficient, β=-0.0088, signifies that, statistically, consuming an additional cup of instant coffee per day leads to a telomere shortening of 0.0088 units.
To facilitate understanding, the team referenced previous practices from Lancet Healthy Longevity and converted the coefficient β into a more interpretable measure. They combined telomere length change with a value of 0.023 (indicating that for every additional year, telomeres shorten by 0.023 units) to transform their coefficient β. Through this conversion (0.0088/0.023=0.38), they arrived at the final figure of "0.38 years" (the impact of consuming an extra cup of instant coffee per day on telomere length, equivalent to aging by 0.38 years concerning telomere length).
However, it's essential to note that 0.023 is a value derived by researchers after adjusting for multiple confounding factors in the relationship between telomere length and lifespan. In reality, telomere length and lifespan are influenced by various factors.
Furthermore, the study results only pertain to the relationship between instant coffee and telomere length. Therefore, interpreting 0.38 years as a direct relationship between instant coffee and lifespan would be inaccurate. Wei Yudong emphasized that despite referencing previous literature, this is merely a correlation, not a causation.
"0.38 years is an indirect conversion, not a straightforward indicator of lifespan shortening by 0.38 years," added Shen Mingwang. Moreover, the study utilized a 24-hour dietary recall questionnaire, meaning "daily consumption" should be understood as "the average increase in daily intake."
According to Shen Mingwang, the relationship between telomere length and lifespan is complex and influenced by various factors. Even the study on the relationship between instant coffee and telomere length is based on extensive, ongoing, typical samples. Therefore, there's no need to panic about instant coffee based on this research alone.
Following the publication of the team's findings last year, there were misleading reports by some media, claiming that "each cup of instant coffee consumed shortens lifespan." Shen Mingwang clarified to the China Science Daily that determining how much telomere shortening corresponds to aging or lifespan reduction is another research topic requiring further investigation. Additionally, since the database used by the team is from the UK, there are differences in genetics, dietary habits, etc., compared to Chinese individuals. Hence, based on current research, no direct causal relationship between coffee and lifespan can be concluded.
As for why instant coffee consumption may lead to telomere shortening, Shen Mingwang speculated that it might be related to some ingredients in instant coffee, especially additives like creamer and flavorings. However, this remains speculative, and more research is needed for confirmation.
