Nearly 500k-person study reveals heavy smoking speeds aging

Shortening the length of leucocyte telomere

Researchers found that individuals smoking higher amounts of cigarettes are more likely to experience shortening of leucocyte telomere. The length of these end fragments is called telomere. Shortening the white blood cell telomeres indicates aging and poor cell health.

A statement by the researchers says that smoking shortens the end fragments of chromosomes in the white blood cells of our immune systems. 

Dr. Siyu Dai, assistant professor at the School of Clinical Medicine, Hangzhou Normal University, and an honorary postdoctoral researcher in the department of pediatrics at The Chinese University of Hong Kong, executed the study along with her colleague Dr. Feng Chen from The Chinese University of Hong Kong. 

Dr. Dai stated: “Our study shows that smoking status and cigarette quantity can result in the shortening of leucocyte telomere length, which is an indicator of tissue self-repair, regeneration, and aging. In other words, smoking can accelerate the process of aging, while quitting may considerably decrease the related risk.”

Alluding to telomeres, the statement describes them as the plastic or metal sheathes at the end of shoelaces, which prevent the laces from fraying. Similarly, telomeres are a region of repetitive DNA sequences at the end of chromosomes that protect them from fraying. 

The process insinuates the aging of cells naturally; when cells divide, the telomeres become slightly shorter, but when it's shorter to a certain length, they cannot divide any further – instead, the cells die.

Despite scientists having discovered the link between diminishing white blood cells – leucocytes to smoking, this study focused on establishing whether smoking status and the number of cigarettes smoked actually generated the shortening in telomere length, unlike past studies.

The scientists looked at various features in participants of the study, including current smokers, former smokers, and those who never smoked. They also checked for the participant's level of addiction to smoking, cigarette consumption quantity, and data on leucocyte telomere length taken from blood tests.

Mendelian randomization technique

They applied Mendelian randomization, a technique using genetic variations (SNPs) inherited from parents, to understand how environmental factors, like smoking, are directly linked to health issues like shorter telomeres. 

This method eliminates the influence of unknown factors, helping researchers determine causation, not just correlation.

Dr. Dai said. “We found that current smoking status was statistically significantly associated with shorter leucocyte telomere length, whereas previous smokers and people who had never smoked didn’t show significantly shorter leucocyte telomere length.”

“Among people who used to smoke, there was a trend towards shorter telomere length, but this was not statistically significant. People who smoked a greater number of cigarettes had significantly shorter leucocyte telomere length,” she added. “In summary, smoking may cause the shortening of leucocyte telomere length, and the more cigarettes smoked, the stronger the shortening effect.” 

Additionally, Dr. Dai noted that observational studies have found a link between shortened leucocyte telomere length and many diseases, such as cardiovascular disease, diabetes, and muscle loss. 

“Our study adds to the evidence that smoking causes aging. As there are clear health benefits of smoking cessation, it is time to include cessation support as well as treatment into daily clinical management to help us create a smoke-free environment for the next generation.”

The scientists will further study the effects of passive smoking on tissue self-repair, regeneration, and aging, particularly in how it could affect children.

Professor Jonathan Grigg, Chair of the European Respiratory Society Tobacco Control Committee, commented:

“Dr Dai and her colleagues, in a study of half a million adults, show a clear association between smoking and reduced telomere length. This study applied Mendelian randomization, a well-known method for providing good levels of evidence and being able to show causal relationships, to support previous, observational studies suggesting that smoking causes aging, while quitting may reverse this effect.”