Figure 1: Tobacco products. Courtesy of The Independent.
Introduction
Over 5000 chemicals can be found in tobacco smoke often having devastating carcinogenic, respiratory, or circulatory effects on the human body. The most common tobacco smoke caused deaths include cardiovascular disease, chronic obstructive pulmonary disease as well as various types of cancers, making it one of the most significant sources of toxic chemical exposure to humans.[1] The question is: What is it about these chemicals that make tobacco smoke so dangerous?
Nicotine
One of the most infamous chemicals when it comes to tobacco is nicotine (C10H14N2), particularly due to its role as the chief addictive ingredient in tobacco products. The addictive effect of nicotine is due to its binding and activation of nicotinic acetylcholine receptors in the brain, triggering the release of dopamine – the ‘feel good’ hormone – and resulting in a continued desire for that pleasure response.[2] The more tobacco smoked inhaled, the more receptors are formed and the greater the craving for nicotine.
Furthermore, nicotine has the ability to be rapidly absorbed and transported around the body, making tobacco products one of the most effective methods of nicotine administration and further facilitating the addiction. The speed of absorption of nicotine across biological membranes is affected by the pH or its acidity. Since nicotine is a weak base and the smoke from the more commonly used air-cured tobacco products is more alkaline, a lot of nicotine is unionised (has no ions), resulting in a higher rate of pulmonary absorption in the lungs.[3] The rapid distribution of nicotine enables its almost immediate effect as a stimulant as it is transported to the adrenal glands, stimulating the release of adrenaline and resulting in increased heart rate and blood pressure. In addition, as nicotine flows through the bloodstream, this could result in the constriction of arterial walls as well as the increase in the stickiness of platelets, potentially risking the increased formation of blood clots and triggering heart attacks or strokes.[4]
Carbon Monoxide
Another chemical found in tobacco products is carbon monoxide (CO). Instead of oxygen, carbon monoxide binds to haemoglobin to form carboxyhaemoglobin (COHb), limiting the oxygen supply to respiring tissues and lead to slight oxygen deprivation which could cause dizziness and breathlessness but in more extreme cases, carbon monoxide poisoning. Carbon monoxide binds to the same four haem groups as oxygen in haemoglobin. However, whilst the binding of oxygen is reversible, carbon monoxide binds approximately 210 times more tightly. This means that carbon monoxide is released more slowly, thus limiting the available haemoglobin to bind to oxygen. Despite this, the use of supplementary oxygen can take advantage of Le Chatelier’s Principle (or the Law of Equilibrium) to quicken the decomposition of COHb back to haemoglobin.[5]
HbCO + O2 ⇌ Hb + CO2 + O2
Consequences
The chemicals in tobacco smoke can also have a drastic effect on the DNA, triggering dangerous mutations that make a person more susceptible to cancers.[4] For example, although formaldehyde can be found naturally and is even made in the body in small amounts, it may lead to increased risk of myeloid leukaemia. Formaldehyde is genotoxic and binds to the DNA in white blood cells, causing the formation of DNA adducts (DNA bound to a cancer-causing chemical) as well as damaging DNA repair pathways that reduce formaldehyde toxicity.[6] Furthermore, chemicals such as arsenic and nickel, both of which are components in tobacco smoke can enhance the capacity for other compounds to mutate through crosslinking of DNA or inhibiting DNA repair, further impacting the body’s ability to combat many cancers.[7]
These are just a few examples of the thousands of chemicals in tobacco smoke that have an adverse, and potentially fatal, effect on the body – from affecting the brain to the DNA. Despite this, if someone quits smoking, the body has an amazing ability to recover. Not only do the aforementioned nicotine receptors eventually return to its original number but carbon monoxide levels in the bloodstream stabilise so the capacity to carry oxygen increases and after a few years, the DNA’s ability to repair is restored and the risk of fatal cancer is reduced.[4]
Smoking cessation isn’t an easy process but with the right support, a healthier lifestyle can be achieved.
Additional Resources:
https://www.helpguide.org/articles/addictions/how-to-quit-smoking.htm
https://www.cancer.org/healthy/stay-away-from-tobacco/guide-quitting-smoking.html
https://www.webmd.com/smoking-cessation/default.htm
References:
- Talhout, Reinskje, Thomas Schulz, Ewa Florek, Jan Van Benthem, Piet Wester, and Antoon Opperhuizen. 2011. \”Hazardous Compounds In Tobacco Smoke\”. International Journal Of Environmental Research And Public Health 8 (2): 613-628. doi:10.3390/ijerph8020613. [Date Last Accessed]: 30th May 2020
- Picciotto, M. 2000. \”Nicotinic Receptors In The Brain Links Between Molecular Biology And Behavior\”. Neuropsychopharmacology 22 (5): 451-465. doi:10.1016/s0893-133x(99)00146-3. [Date Last Accessed]: 30th May 2020
- Benowitz, Neal L., Janne Hukkanen, and Peyton Jacob. 2009. \”Nicotine Chemistry, Metabolism, Kinetics And Biomarkers\”. Handbook Of Experimental Pharmacology, 29-60. doi:10.1007/978-3-540-69248-5_2. [Date Last Accessed]: 30th May 2020
- Krishna, Sudhir. 2018. \”How Do Cigarettes Affect The Body? – Krishna Sudhir\”. TED-Ed. https://ed.ted.com/lessons/how-do-cigarettes-affect-the-body-krishna-sudhir#review. [Date Last Accessed]: 30th May 2020
- \”Carboxyhemoglobin\”. 2020. En.Wikipedia.Org. https://en.wikipedia.org/wiki/Carboxyhemoglobin. [Date Last Accessed]: 30th May 2020
- \”Formaldehyde\”. 2020. Cancer.Org. https://www.cancer.org/cancer/cancer-causes/formaldehyde.html. [Date Last Accessed]: 30th May 2020
- Dong, Jin-Tang, and Xian-Mao Luo. 1994. \”Effects Of Arsenic On DNA Damage And Repair In Human Fetal Lung Fibroblasts\”. Mutation Research/DNA Repair 315 (1): 11-15. doi:10.1016/0921-8777(94)90022-1. [Date Last Accessed]: 30th May 2020