What is smoking and why do people do it?

Smoking of dried tobacco leaves has been, and continues to be, an addictive pastime practiced all over the world. More recently, this has been superseded by e-device inhalation (vaping) of pure nicotine extracts and other substances. For centuries, tobacco leaves have been dried, cut up and burned within loaded devices designed for oral inhalation of the smoke (i.e., smoking).

The tobacco leaf is high in a substance called nicotine, which provides a stimulatory effect to the brain by activating special receptors and increasing the residency time of the brain hormone, dopamine. This hormone has a rewarding effect [1] that forms part of the addictive and habit-forming behavior with smoking and associated social activities. The fact that tissue damage is gradual, and smoking is not instantly damaging leads to a feeling of complacency (i.e. being in a “comfort zone”), which also reinforces the habit.

Why is smoking harmful to health?

Commercial cigarettes, when burned, release a cocktail of an estimated 8000 different chemical compounds, including those from the plant itself and other additives [2]. Although some of the plant derived compounds have on their own been reported to have a positive effect on human health, such as stress relieving and concentration improvement, other compounds are toxic to many organs in the body, including the vital organs – lungs, heart, blood vessels and brain. For example, arsenic, cadmium, lead, acetone and ammonium are known to be neurotoxic, cancer causing (carcinogenic) and gene damaging (mutagenic and genotoxic) chemicals [3].

The lungs are most at risk, because the tobacco smoke condenses inside the airways after the nicotine and other bioactive compounds have been absorbed into the bloodstream. What is left over time is a kind of thick sludge called tar that causes lung inflammation, oxidative stress damage and kills lung cells. Over time, this decreases lung capacity by forming scar tissue, and increases the chance of respiratory infections. Smoking causes a 2-4-fold increased risk of stroke, a problem related to clots forming in the lungs that travel into the brain and block blood vessels

Effects on aging around the body

Smoking has been estimated on average to decrease the smoker’s life expectancy by about 10 years [4], and also damages the health of people around them who breathe in the smoke second-hand (passive smoking). So, in the case of serious health problems, this would obviously cause an effect on aging, particularly in the vital organs.

However, the effects of smoking in other organs of the body, despite being less severe or obvious, indicate a premature aging effect [5]. We often notice the skin of smokers to be more wrinkled, dry, discolored, red or porous compared to non-smokers, depending on the smoker’s ethnicity. In fact, these changes occur from within because of degradation of collagen and breakdown of connective tissue,  which normally occurs more gradually over time during natural aging.

In the reproductive system, cigarette smoke causes genetic and metabolic problems in sperm formation [6]. This leads not only to difficulties conceiving but may result in the damage being pass on to the next generation. Sperm are also very susceptible to oxidative stress and even low-level toxicity in the body, despite the smoker feeling reasonably healthy.

Tobacco smoke causes different types of physical and chemical damage to the blood vessels all over the body [7]. Especially in the smaller vessels of the lungs, eyes, skin, kidneys and brain. Nicotine has a vasoconstricting (size reduction) effect that is short-lived, but over time this, in combination with tissue damage, can lead to a range of blood vessel blockages [8]. Nicotine from tobacco smoke increases blood sugar levels around the body, and combined with the blood vessel damage, may contribute to type 2 diabetes risk, metabolic imbalances and longer-term weight problems.

Finally, tobacco smoking has been linked to the accelerated formation of different types of cancer in different parts of the body, mainly in the lungs, nose, mouth and throat [9]. Cancers are simply growths of tissues that changed from normal growth to uncontrolled growth, because of damage to their genetics, epigenetics or energy production processes, at the cellular level. Although they form slowly, smoking may speed them up.

Mechanisms involved in accelerating the ageing process

In summary, some of the main impacting mechanisms of tobacco smoking include:

• Oxidative stress
• Nitrosative stress
• Cell and tissue toxicity
• Genetic toxicity
• Epigenetic disturbances

Take home

Smoking can cause damage that is akin to premature aging, because it is gradual and involves many different processes working together. With all things considered, and looking at all the evidence to date, it has been estimated that even one cigarette can reduce life expectancy by 11 minutes [10]. This may not seem significant, but the ability for the body to recover is limited by how many of these 11-minute impacts a smoker has made throughout their lifetime.

References

1. Wills, L., et al., Neurobiological Mechanisms of Nicotine Reward and Aversion. Pharmacol Rev., 2022. 74(1): p. 271-310. doi: 10.1124/pharmrev.121.000299.
2. Hong, S.W., et al., Biologically Active Compounds Present in Tobacco Smoke: Potential Interactions Between Smoking and Mental Health. Front Neurosci., 2022. 16:885489.(doi): p. 10.3389/fnins.2022.885489. eCollection 2022.
3. https://www.lung.org/quit-smoking/smoking-facts/whats-in-a-cigarette.
4. West, R., Tobacco smoking: Health impact, prevalence, correlates and interventions. Psychol Health., 2017. 32(8): p. 1018-1036. doi: 10.1080/08870446.2017.1325890. Epub 2017 May 28.
5. Morita, A., et al., Molecular basis of tobacco smoke-induced premature skin aging. J Investig Dermatol Symp Proc., 2009. 14(1): p. 53-5. doi: 10.1038/jidsymp.2009.13.
6. Esakky, P. and K.H. Moley, Paternal smoking and germ cell death: A mechanistic link to the effects of cigarette smoke on spermatogenesis and possible long-term sequelae in offspring. Mol Cell Endocrinol., 2016. 435:85-93.(doi): p. 10.1016/j.mce.2016.07.015. Epub 2016 Jul 14.
7. Messner, B. and D. Bernhard, Smoking and cardiovascular disease: mechanisms of endothelial dysfunction and early atherogenesis. Arterioscler Thromb Vasc Biol., 2014. 34(3): p. 509-15. doi: 10.1161/ATVBAHA.113.300156.
8. https://www.cdc.gov/diabetes/library/features/smoking-and-diabetes.html#:~:text=Over%20time%2C%20high%20blood%20sugar, u.o.y.a.w.
9. https://www.cancercouncil.com.au/news/there-are-16-cancers-that-can-be-caused-by-smoking/.
10. Shaw, M., R. Mitchell, and D. Dorling, Time for a smoke? One cigarette reduces your life by 11 minutes. BMJ., 2000. 320(7226): p. 53.

from an Expert Author

George Thouas

BSc, MRepSc, PhD – Biomedical Scientist

George has worked as a medical researcher for 17 years in the university sector, at both Monash University health institutes, and The University of Melbourne. He spent 12 of those years in reproductive health and fertility research, in roles such as Clinical Research Associate, Clinical Embryologist, Post-graduate Demonstrator, Lecturer, and later as a Senior Research Fellow and Lab Manager. His doctoral thesis investigated the effects of mitochondrial damage in the oocyte. He also worked on improving the nutrient and growth requirements for in vitro fertilization and embryo development.

George has authored and coauthored more than 50 publications, including 1 book, 5 book chapters, 30 peer-reviewed journal reports and reviews, 6 patents, international scientific conference proceedings and health practitioner journal articles.

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