Not just dogs linked to snoring

Research has found that “children growing up with a pet dog in the house are more likely to be heavy snorers as adults”, The Daily Telegraph reports. The newspaper says the study also found that growing up in a large family or suffering from respiratory or ear infections as a toddler were more likely to make you a snorer in later life.

This study found associations between various factors and snoring in later life. Some results were unsurprising, such as strong links between snoring and smoking and obesity. It also found links to some unexpected factors, including babies that lived in households with dogs were 26% more likely to snore as adults. However, the study has a number of limitations: it assessed snoring by questionnaire, relied on people’s childhood recollections, and  categorised the responses into broad groups. Despite the large number of people who took part, associations found in a cross sectional survey do not prove causation. The results suggest there may be a number of factors that influence whether a person snores and it is not caused by any one factor alone.

Where did the story come from?

Professor Karl A Franklin from University Hospital, Umeå, Sweden, and colleagues from various other hospitals and institutions in Sweden, Norway and Iceland, carried out the research. The study was funded by the Swedish Heart and Lung Foundation, and other Swedish, Icelandic, Norwegian, and Estonian research councils and foundations. The study was published in the (peer-reviewed) medical journal: Respiratory Research.

What kind of scientific study was this?

This was a cross sectional study in which the researchers aimed to investigate the associations between the environment during early life and snoring in adulthood.

Between 1999 and 2001, the researchers mailed questionnaires to a sample of people (aged 25 to 54) from population registers in selected cities in Iceland, Norway, Sweden, Denmark, and Estonia. The questionnaire assessed the participants’ sleepiness during the daytime and their loud and disturbing snoring during the last few months. The responses were never, less than once a week, 1-2 days a week, 3-5 days a week, or almost every day. The researchers defined habitual snoring as ‘loud and disturbing snoring at least three nights a week’ and daytime sleepiness as ‘feeling sleepy during the daytime at least 1-2 days a week’. The participants childhood environment was assessed by questions such as their mother’s age at their birth and whether she smoked while pregnant. Other questions asked if there were any pets in the home when they were born or as a child, if they had been hospitalised for respiratory infection before the age of two, their parents’ level of education, and the number of people living in the home before the age of five.

Participants were also assessed on their current health including whether they had had an ‘asthma attack’ in the past 12 months, their current medications, allergies, smoking history, chronic bronchitis, current smoking, estimated BMI and type of housing. The researchers received responses from 16,190 people (74% of those approached). They then used statistical analyses to look at links between the different variables with snoring and daytime sleepiness.

What were the results of the study?

More women than men responded to the questionnaire (53%) and respondents were on average significantly older than non-respondents (40 years). Of these, 18% (2,851 people) were categorised as ‘habitual snorers’. Compared to non-snorers, habitual snorers were significantly more likely to be older, male, to have higher BMI, to smoke, and to have self-reported asthma or chronic bronchitis. Fewer snorers reported that either parent had been educated to university level. Habitual snorers were also significantly more likely to have:

• reported hospitalisation for respiratory infection before age two,
• ear infections in childhood,
• a dog at home when they were newborn or a child,
• a cat or other pet at home when newborn, and
• greater than five people living in the house as a child.

When the risk figures were calculated, participants who had a dog at home as a baby had an increased risk of snoring as an adult of 26%. Other factors that had greater increases in risk for snoring included chronic bronchitis, which increased risk by 133%, and an increase of BMI of 5kg/m2 increased risk by 82%. Other significant increased risks for snoring included being hospitalised for respiratory infection before age two (27%), ear infection (18%), increase in household size by one extra person (4%), allergic rhinitis (22%) and smoking (15%). Similar associations were seen for daytime sleepiness. However, when the researchers looked at ‘the adjusted proportion of snoring that could be explained by different risk factors, calculated as the population attributable fraction (PAF)’ they found that the greatest contributing factors were smoking (PAF 14.1%) and obesity (9.1%). The PAF for being exposed to a dog as a newborn was 3.4%.

What interpretations did the researchers draw from these results?

The researchers conclude that being exposed to a dog as a newborn, having severe respiratory infections or recurrent ear infections in childhood or being from a large family, are environmental factors that are associated with snoring in adult life.

What does the NHS Knowledge Service make of this study?

This research assessed a large number of people and found associations between a number of environmental and personal factors and snoring in adulthood. However, it is important to realise that associations found in a cross sectional survey to not prove causation. In particular, there are a number of limitations surrounding the method of data collection:

• Snoring is not an easy thing to measure subjectively as the typical snorer is less disturbed by the snoring than their partner or other household members. Therefore asking an individual to estimate the frequency and volume or disturbance of their own snoring may not give an accurate indication or reflect the experience of others. Additionally, there is no distinction between those who may have sought medical help or have a diagnosed condition such as obstructive sleep apnoea.
• Snoring was only assessed at one point in time and may vary throughout a person’s lifetime. Therefore, the question of whether childhood factors affect snoring is not easily answered, for example does it have effect an people who only occasionally snore or just on longer-term snoring?
• As the participants answers regarding their childhood were based on what they could remember, there are likely to be some inaccuracies or bias, particularly in questions such as whether they were hospitalised for infection prior to the age of two or ear infections, which a person may not know or remember. It is also unclear how the timing or duration of the exposures was assessed, for example, whether a person was considered to have ear infections if they reported one episode, two, more than five, etc.
• Other medical and lifestyle factors may be associated with snoring and these were not assessed by the questionnaire. Additionally, those assessed may have inaccuracies, for example the participants’ BMI was not actually measured by the researchers.
• Not all questionnaires would have had complete responses to all questions.
• Not all people asked to participate in the questionnaire responded, and this included slightly more men who snore more frequently than women. If these people had responded, the results could have been different.

Although the news stories concentrated on the links to pets, particularly dogs, in the household; the research demonstrated links to numerous factors, smoking and BMI being the factors that contributed the greatest risk. This suggests that there may be a number of factors that influence whether a person snores or not. Based on the findings of this research alone, people should not be overly concerned about having a dog around their baby or child.