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A Good Night's Sleep

Air pollution might be linked to poor sleep, say researchers looking into the impact of toxic air on our slumbers. Q.1 The study explored the proportion of time participants spent asleep in bed at night compared with being awake - a measure known as sleep efficiency. The results reveal that greater exposure to nitrogen dioxide and small particulates known as PM 2.5s are linked with a greater chance of having low sleep efficiency. That, researchers say, could be down to the impact of air pollution on the body.

'Your nose, your sinuses and the back of your throat can all be irritated by those pollutants so that can cause some sleep disruption,' said Martha Billings, assistant professor of medicine at the University of Washington and co-author of the research. The study drew on air pollution data captured for nitrogen dioxide and PM2.5 levels over a five-year period in six US cities, including data captured near the homes of the 1,863 participants. Q.2 The data was then used to provide estimates of pollution levels in the home.

From the results, Q.3 the team grouped the participants according to their sleep efficiency, finding that the top quarter of the participants had a sleep efficiency of about 93% or higher, while the bottom quarter had a sleep efficiency of 88% or less. The team then took all of the participants and split them into four groups based on their exposure to air pollution. After taking into account a host of factors including age, smoking status and conditions such as obstructive sleep apnea, the team found that those who were exposed to the highest levels of air pollution over five years were more likely to be in the bottom group for sleep efficiency than those exposed to the lowest levels.

More specifically, high levels of nitrogen dioxide increased the odds of having low sleep efficiency by almost 60%, while high levels of PM2.5s increased the odds by almost 50%. Higher levels of pollution were also linked to greater periods of time spent awake after going to sleep. However, Q.4 it is not clear whether the pollution itself was affecting the participants' sleep or whether the poorer sleep quality might be down to other factors linked to pollution, such as the noise generated by traffic. In addition, data from one week's sleep might not reflect an individual's typical sleep pattern.

Scott Weichenthal, an epidemiologist from McGill University in Canada, who was not involved in the study, said Q.5 the research did not prove that air pollution caused poor sleep, but he added that Q.6 'There is certainly increasing evidence that air pollution affects our body in ways that we didn't appreciate before.' Roy Harrison, professor of environmental health at the University of Birmingham, said a link between pollution and sleep was not unexpected. 'Previous research has shown associations between nitrogen dioxide exposures and effects upon various physiological and biochemical functions in the body, as well as hospital admissions and mortality,' he said. 'It should therefore come as no surprise that such exposures also affect sleep patterns.'

The Tribune


1) The writer defines sleep efficiency in the first paragraph as

  • A) the amount of time spent sleeping in bed to all the time during the day and night spent awake.
  • B) the ratio of the time spent sleeping in bed to all the time during the day and night spent awake.
  • C) the hours spent trying to sleep including naps to all the time spent not sleeping.
  • D) the ratio of all time spent trying to sleep to time spent actually sleeping.


2) What reference information does the writer tell us the researchers used as a basis for their study, in the second paragraph?

  • A) The levels of nitrogen dioxide in the house over time.
  • B) The levels of PM2.5 in the house over time.
  • C) The levels of nitrogen dioxide and PM2.5 in the house over time.
  • D) The levels of nitrogen dioxide and PM2.5 and a host of other contaminants in the house over time.


3) Why does the writer explain the way in which the researchers separated the participants into different groups?

  • A) To show that it made the research easier to control.
  • B) To illustrate how the research was more balanced.
  • C) To explain how the researchers wanted to compare the effects of different parameters.
  • D) To show the research was easy to explain.


4) What does the writer imply about the study's conclusions?

  • A) Sleep patterns are affected by age and gender.
  • B) Pollution may not be the only cause of sleep quality.
  • C) Data from one week's sleep is enough to predict patterns.
  • D) Higher levels of pollution do not affect sleep quality.


5) The writer quotes the opinion of other scientists not involved in the study to

  • A) show that some experts feel the data didn't prove a casual relationship between sleep efficiency and pollution.
  • B) demonstrate the research was poorly done.
  • C) explain the size of the group was inadequate.
  • D) state the study should be repeated.


6) The writer seems to suggest that

  • A) experts all agree that analysing sleep patterns is difficult.
  • B) it is said that pollution affects people's ability to concentrate.
  • C) pollution affects how the human body behaves.
  • D) all scientists believe that sleep patterns need to be studied.