How Smoking Affects Muscle Function and Body Composition?
To commemorate the 35th World No Smoking Day on 31/05/2021, we thought we would examine how smoking affects body composition and muscle function. Cigarette smoking is directly responsible for the deaths of up to 7 million people a year worldwide (one person every 5 seconds), according to the World Health Organisation (1). Smoking is a well understood major risk factor for cardiovascular disease (2), respiratory disease (3), cancer (4), and more severe COVID-19 related outcomes (5).
Smoking cigarettes is different from other lifestyle risk factors (e.g., not doing enough physical activity), because it has a chemical dependency effect on our brains. The nicotine contained within tobacco products causes people to become addicted, making it very difficult to quit smoking. Nevertheless, the proportion of UK adults who routinely smoke cigarettes has drastically reduced from 20.2% in 2011 to 14.1% in 2019 (6). Whilst this is promising, it does still unfortunately mean 7.2 million adults in the UK are still active smokers. This is despite the risks of smoking being routinely posted on the packaging of tobacco products (slogans like ‘smoking kills’ and ‘smoking causes heart attacks’). This does beg the question, why are 10% of the UK adult population still smoking?
Immediate benefit vs long-term risk
One key reason smokers continue is that they perceive the benefits of smoking to outweigh the risks (7). Nicotine administration does provide acute stimulatory benefits like improved fine motor control (e.g., handwriting), increased attention, enhanced short-term memory capacity, and improved mood (relief from nicotine withdrawal) (8). Unlike such benefits, the disastrous effects of cigarette smoking generally become more evident later in life (9), which is referred to as the ‘smoking time bomb’.
The greatest proportion of current UK smokers (~20%) are now aged between 25 and 34 (6). Many individuals within this group may conclude they will suffer the consequences from their smoking habit in the future, but not right now. This unfortunate perception about a lack of short-term consequences, deters many smokers from trying to cut down or better yet quit smoking altogether.
Throughout this article we want to explore the underappreciated short-term consequences of cigarette smoking. Viewing this topic purely from a fitness perspective, a greater emphasis will be placed on body composition, and muscle function.
Short-term effects of cigarette smoking on body composition
From the early 1970’s onwards, cigarette companies have tried to align smoking advertisements with appearance benefits like beauty, and the promise of a lower body weight (10). This has led many appearance motivated individuals to either continue, or perhaps, even more concerningly, consider starting to smoke cigarettes (11).
Lower muscle mass: Ironically, cigarette smoking is actually linked with a reduction in body mass index (BMI), and thus body weight (12). However, such a reduction in BMI does not represent a reduction in fat mass, but instead a reduction in muscle mass. Smoking stops new muscle proteins being synthesised and causes existing muscle proteins to be broken down (13). In-fact, compared to non-smokers, smokers have a 25% smaller vastus lateralis fibre cross sectional area (13). This is mostly due to higher levels of localised muscle inflammation, and reduced transport of proteins into muscle tissue (13).
Higher stomach fat: Smoking is also linked with an increase in stomach fat (14). Those who smoke more than 20 cigarettes per day have a 7cm greater waist circumference, and a 48% higher level of stomach fat, compared to those who smoke less than 20 cigarettes per day (15). Reduced muscle mass in the abdominal region (caused by smoking), is gradually infiltrated by and replaced with fat tissue (16). Increased central fat storage further increases localised inflammation and reduces muscle tissue. This detrimental cyclical process gradually increases stomach fat and waist circumference in those who smoke.
Beginning/ continuing to smoke cigarettes for the purposes of body composition management therefore appears to be counterintuitive. In contrast, 12 weeks of smoking cessation is linked with gains in lean body mass of ~1.26kg (compared to those who continue to smoke) (17), as-well as a 16% reduction in stomach fat (15).
Short-term effects of cigarette smoking on muscle function
In the UK, around 1 in 4 people in manual occupations smoke, and around 1 in 3 smokers are physically active (18). As such, the effects of cigarette smoking on muscle function are highly important and should be made clear to such individuals.
Increased muscle fatiguability: Unsurprisingly, cigarette smoking is linked with increased muscle fatiguability, meaning smokers muscles tend to get tiered quicker compared to non-smokers (13). Ironically, 2 out of 3 smokers are physically inactive (18), due to the uncomfortable experience of muscle fatigue/ tiredness that presents during exercise. Compared to non-smokers, inactive smokers experience a reduction in type 1 muscle fibres (slow-twitch) which causes muscle fatigue (13). Aside from inactivity, smoking causes muscle fatiguability on its own by reducing:
• blood flow to the muscle (reducing transport of oxygen and nutrients)
• oxygen binding to hemoglobin/ mitochondrial entry (due to carbon monoxide build up)
• adenosine triphosphate production by muscle mitochondria
• muscle mitochondrial structural integrity (increasing production of harmful reactive oxygen species within muscle)
Maximal muscle strength: In contrast to muscle fatiguability, the effects of smoking on muscle strength are less clear. Smoking may actually enhance one’s ability to voluntarily activate a muscle with their brain, thus increasing force output (19). Nicotine appears to be similar to the way caffeine stimulates sympathetic nerve activity (20). However, this effect appears very acute and small in magnitude, with the chronic reduction in muscle fibre size (especially fast-twitch type 2 fibres), and general muscle wasting gradually reducing maximal muscle strength over the moderate term in smokers (13). In-fact, between the ages of 21-36, smoking more than 10-15 cigarettes per day is linked with a reduction in leg muscle strength of around 2.5-5% (21). Put simply, if you can squat 200kg for one rep when you are 21, smoking 10-15 cigarettes per day could cause this to drop to 190-195kg by the time you are 36, even if you trained perfectly for 15 years.
Therefore, physically active smokers, as-well as those smokers working in manual occupations, should be aware that smoking cigarettes is likely affecting their ability to engage in high functioning physical work. In contrast smoking cessation, appears to improve mitochondrial function, and muscle function (13). Improvements in muscle function may in turn lead to greater physical activity and better all-round related outcomes for smokers.
Conclusion and Recommendations
Smokers perceive a lack of short-term consequences, but may be unaware that they are at increased risk of muscle mass loss, increased stomach fat, increased muscle fatiguability, and reduced muscle strength. Unlike the well documented long-term health consequences, such downsides do seem to impact a person sooner, and thus may be of greater consideration for smokers considering quitting.
Thankfully there does appear to be real measurable benefits to smoking cessation, with regards to body composition and muscle function. There also appears to be a real benefit to cutting down cigarette consumption to <20 per day, and preferably <10 per day. There are a number of practical steps that can be taken, including the following 3 recommendations:
1. Cut down: Try to cut down the number of cigarettes smoked per day (below 10-20 per day) to reduce the harmful effects of smoking on body composition and muscle function
2. Get moving: As muscle function improves following cutting down, try to get a bit more active
3. Stop smoking: Try to stop smoking entirely to maximally reduce the harmful effects of smoking on body composition and muscle function
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