Each cigarette smoked a day by heavier smokers increases the risk of contracting some diseases by more than 30%, according to an international study led by the Australian Centre for Precision Health based at the University of South Australia.
The study links heavier smoking* with 28 separate health conditions, revealing a 17-fold increase in emphysema, 8-fold increase in atherosclerosis (clogged arteries) and a 6.5-fold higher incidence of lung cancer, according to University of South Australia material dated 7 August 2020.
The findings, published in EClinicalMedicine, analysed hospital data and mortality statistics from more than 152,483 ‘ever smokers’ in the UK Biobank to look how heavier smoking affects disease risks.
Chief Investigator Professor Elina Hypponen at the University of South Africa says the risk of suffering respiratory diseases, cancers and cardiovascular diseases increased with each cigarette smoked per day.
The links between heavier smoking and emphysema, heart disease, pneumonia and respiratory cancers were particularly high, but the researchers also found associations with many other respiratory diseases, renal failure, septicaemia, eye disorders, and complications of surgery or medical procedures.
Smoking snapshot
"Tobacco smoking is the leading preventable cause of death worldwide and smokers typically die 10 years earlier than non-smokers," Hypponen says.
"Despite a global decline in smoking over the last 20 years, an estimated 20% of the world's population aged over 15 years are still smoking tobacco."
In the United States alone, smokers number 40 million, with 16 million of those living with a disease caused by smoking. This costs their economy more than $300 billion per annum," Hypponen says.
The most recent statistics from Australia show that about 13.8% of its adult population (2.6 million people) are daily smokers. Despite a 10% reduction since 1995, smoking is estimated to kill 19,000 Australians a year, accounting for 9% of the total burden of disease and $137 billion in annual medical costs.
Several known smoking outcomes, including stroke, were not identified in the study, which only counted cases above 200 for each health condition.
"We only looked at how heavier smoking further affects diseases risks in a group of people who are all at least past smokers, so compared to never smokers, the health effects are going to be even more notable.
“Other factors, including when people start smoking or how long they have smoked, may also affect the health consequences arising from smoking," Hypponen says.
"In the past 20 years, the proportion of people smoking a pack or more per day has decreased in countries such as the US and Australia, while there has been an increase in those smoking less than 10 cigarettes per day.
"While this reflects progress, our study shows that each additional cigarette smoked matters, notably increasing the risks of cancer, respiratory, circulatory and many other diseases."
* A daily smoker is classified as someone who smokes regularly, at least one cigarette a day. Light smokers on average smoke less than 10 cigarettes a day, moderate smokers 10 to 19 cigarettes a day and 20 or more cigarettes a day is classified as heavy smoking.
Mendelian randomization case-control PheWAS in UK Biobank shows evidence of causality for smoking intensity in 28 distinct clinical conditions.
EClinicalMedicine. Published 31 July 2020.
Authors
Professor Elina Hypponen, Dr Catherine King, Dr Anwar Mulugeta, Farhana Nabi and Ang Zhou – all from the Australian Centre for Precision Health, University of South Australia – and Professor Robert Walton from Queen Mary University of London.
Abstract
Smoking is one of the greatest threats to public health worldwide. We integrated phenome-wide association study (PheWAS) and Mendelian randomization (MR) approaches to explore causal effects of genetically predicted smoking intensity across the human disease spectrum.
Methods
We conducted PheWAS case-control analyses in 152,483 ever smokers of White-British ancestry, aged 39–73 years. Disease diagnoses were based on hospital inpatient and mortality registrations. Smoking intensity was instrumented by four genetic variants, and disease risks estimated for one cigarette per day heavier intakes. Associations passing the FDR threshold (p<0•0025) were assessed for causality using several complementary MR approaches.
Findings
Genetically instrumented smoking intensity was associated with 48 conditions, with MR supporting a possible causal effect for 28 distinct outcomes.
Each cigarette smoked per day elevated the odds of respiratory diseases by 5% to 33% (nine distinct diseases, including pneumonia, emphysema, obstructive chronic bronchitis, pleurisy, pulmonary collapse, respiratory failure) and the odds of circulatory disease by 5% to 23% (seven diseases, including atherosclerosis, myocardial infarction, congestive heart failure, arterial embolisms).
Further effects were seen for cancer within the respiratory system and other neoplasms, renal failure, septicaemia, and retinal disorders. No associations were observed in sensitivity analyses on 185,002 never smokers.
Interpretation
These genetic data demonstrate the substantial adverse health impacts by smoking intensity and suggest notable increases in the risks of several diseases. Public health initiatives should highlight the damage caused by smoking intensity and the potential benefits of reducing or ideally quitting smoking.
[link url="https://www.sciencedaily.com/releases/2020/08/200807102335.htm"]Heavier smoking linked to skyrocketing health risks[/link]
[link url="https://www.thelancet.com/journals/eclinm/article/PIIS2589-5370(20)30232-7/fulltext"]Mendelian randomization case-control PheWAS in UK Biobank shows evidence of causality for smoking intensity in 28 distinct clinical conditions[/link]