The discussion above may give the impression that the ill effects of smoking only become evident in old age. This is not the case. Cancers may begin to occur in people aged in their 30s, if they have been smoking for 15-20 years.(55) The influence of smoking on heart disease is much greater at younger ages.(55) In smokers between 35-44 years of age, 73% of deaths from coronary heart disease are due to smoking. By ages 75-84 years, the proportion of CHD deaths due to smoking in current smokers falls to 14%.(55)
Even smoking one cigarette causes a wide range of physiological reactions. The nicotine in cigarettes causes changes in heart rate. Blood pressure rises and peripheral blood circulation slows, resulting in lowered skin temperature. Changes occur in brain waves, a number of endocrine and metabolic effects are triggered, and skeletal muscle relaxation occurs.(56) Addiction to nicotine can occur at an early age, and young people have reported withdrawal symptoms and difficulty in quitting.(57)
The carbon monoxide inhaled when a cigarette is lit has a number of toxic effects on the body, the most immediate of which is its impairment of oxygen transportation in the blood. As carbon monoxide has a chemical affinity for haemoglobin over 200 times greater than that of oxygen, it binds preferentially with the haemoglobin, and reduces the amount of oxygenated blood circulated to body organs and tissues.(13) This impairs muscular performance, and may also affect the vision, particularly at altitude (see Section 3.6 below).
In general, smokers are less fit than non-smokers, performing less well in both endurance and short term exercise. Smokers are slower, reach exhaustion earlier, and achieve lower goals.(57) These disadvantages are directly related to duration of smoking and amount smoked, and are caused by the adverse effects of carbon monoxide on blood oxygen levels, as well as increased heart and metabolic rates stimulated by smoking.(57)
A recent study found that atherosclerosis begins in childhood and progresses from fatty streaks to raised lesions in adolescence and young adulthood. Smoking is associated with more extensive fatty streaks and raised lesions in the abdominal aorta of this age-group.(57a)
Toxic chemicals in cigarette smoke damage the lung capacity and clearance function, leading to increased coughs and respiratory infections among smokers.(38) Adolescent smokers cough more than adolescent non-smokers, and by the time they reach young adulthood, a substantial proportion of them will have abnormal changes in the cellular structure of their small airways.(38) Teenage smokers also experience more asthma and allergic symptoms than non-smokers of the same age,(58) suffer a greater degree of shortness of breath on exertion,(59) and develop more respiratory tract infections than non-smokers.(57)
Smokers on average suffer poorer health than non-smokers, and are more likely to miss school(57) or work due to illness(60,61) (see also Section 3.15 below, and Chapter 6, Section 8).