Wednesday March 5 2014
Passive smoking is known to increase risk of cot death
“Passive smoking causes lasting damage to children's arteries, prematurely ageing their blood vessels by more than three years,” BBC News reports.
The news is based on emerging evidence that exposure to secondhand smoke damages children’s arteries. This news is concerning, as the thickening of blood vessel walls (atherosclerosis) is known to increase the risk of heart attacks and strokes in later life.
Parents of approximately 3,700 children from Finland and Australia were asked if neither, one or both parents smoked.
Up to 25 years later, the grown-up children underwent ultrasound scans on the large carotid arteries in their necks, to estimate their carotid intima media thickness (IMT). A high IMT can indicate the flow of blood through the carotid arteries to the brain, which can potentially become blocked, triggering a stroke.
The researchers found that having a high carotid IMT in adulthood was significantly more likely in those who were exposed to both parents smoking. However, having only one parent who smoked was not linked to increased greater carotid IMT in adulthood.
The study does have limitations, including its reliance on self-reporting; however, the results add to already existing evidence that exposing children to passive smoking can increase the risk of both short-term and long-term conditions.
Where did the story come from?
The study was carried out by researchers from the University of Tasmania in Australia and the Universities of Turku and Tampere in Finland, along with other Australian and Finnish institutions. It was funded by various organisations: the Commonwealth Departments of Sport, Recreation and Tourism, and Health; the National Heart Foundation; the Commonwealth Schools Commission; the National Health and Medical Research Council; the Heart Foundation; the Tasmanian Community Fund; and Veolia Environmental Services.
The study was published in the peer-reviewed European Heart Journal and is available on an open access basis, so it is free to read online or download.
Both BBC News and the Mail Online website provide an accurate summary of the study.
What kind of research was this?
This study was a secondary analysis of two independent long running prospective studies carried out in Australia and Finland, which followed participants for up to 25 years.
The aim was to assess the role of exposure to parental smoking in children or adolescence on carotid IMT in adulthood.
What did the research involve?
The study involved 2,401 children from Finland (aged 3-18 years) and 1,375 children from Australia (aged 9-15 years), with a follow-up of up to 25 years. The Finnish study also analysed the association between cumulative exposure to parental smoking for 3 years and carotid IMT in adulthood.
In both studies, researchers determined the self-reported smoking status of the participant’s parents at the beginning of the studies. Parental smoking was reported as:
- neither parent
- one parent
- two parents
Self-reported current smoking status of the participants (children) was also recorded at the beginning of the study. Questionnaires also gathered other information on the participants, including height, weight (to calculate their body mass index) and physical activity level.
At follow up (up to 25 years later), questionnaires gathered information on the participant’s total years of schooling, current smoking status, physical activity levels, alcohol consumption and cardiovascular risk factors.
At follow up, ultrasound measurements were carried out on the participants (who were now adults) to measure the thickness of their carotid artery walls (IMT). The carotid IMT measurements were made by members of the research team, as they did not know whether the participants had been exposed to passive smoke during childhood.
What were the basic results?
The main findings of this study were that:
- carotid IMT in adulthood was significantly greater in those exposed to both parents smoking in childhood compared to those whose parents did not smoke (adjusted marginal means 0.647 mm (standard deviation (0.022) vs. 0.632 mm (standard deviation 0.021). This association remained significant after adjustment for all potential confounders of both the participants and parents including age, sex, parental education and the child’s smoking status at the start of the study and at follow up.
- cardiovascular risk factors of the participants in adulthood were also considered in the adjustments
- having just one parent (mother or father) who smoked was not linked to carotid IMT in adulthood (pooled analysis of both studies)
- in one of the studies, greater exposure to parental smoking over a three-year period was linked to a significantly greater carotid IMT in adulthood
The researchers determined that the effects of exposure to both parents smoking on participants’ vascular age was equivalent to being 3.3 years older (95% confidence interval (CI) 1.31 to 4.48) than the participants actual age in adulthood (pooled analysis of both studies).
How did the researchers interpret the results?
The researchers concluded there is an extensive effect of exposure to parental smoking on children’s vascular health up to 25 years later. They state that there must be continued efforts to reduce smoking among adults, in order to protect young people and to reduce the prevalence of cardiovascular diseases, such as heart attacks, across the population.
Dr Seana Gall, one of the researchers from the Menzies Research Institute Tasmania, is reported in the media as saying: "Our study shows that exposure to passive smoke in childhood causes a direct and irreversible damage to the structure of the arteries."
They went on to say that: "Parents, or even those thinking about becoming parents, should quit smoking. This will not only restore their own health, but also protect the health of their children into the future."
Overall, this secondary analysis study provides preliminary evidence of the effects of parental passive smoking on the artery walls of children and adolescents in adulthood.
The researchers attempted to adjust for potential factors that could influence risk (confounders), such as:
- smoking status
- physical activity levels
- alcohol consumption
- schooling level of the parent(s)
In their analysis, they also took into consideration cardiovascular risk factors of the participants in adulthood.
There are some limitations to the study, which are worth noting. Parental smoking status was self-reported and not objectively measured by the researchers, so there is a possibility that parents did not have accurately reported their actual smoking status. This is also the case for the reporting of the participants’ smoking status. The study was a secondary analysis of two larger cohort studies, so it’s likely that the cohorts themselves did not have the same outcome of interest as the current study.
Despite these limitations, however, there is a substantial body of evidence that shows that passive smoking is harmful, especially when those involved are children. Tobacco smoke contains around 70 cancer causing chemicals and hundreds of other toxins.
If you do choose to smoke, you should do it outside and well away from your children. There is plenty of free advice and treatment that could help you kick the habit.
Analysis by Bazian. Edited by NHS Choices.
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