Smoking and a high dietary salt intake significantly increase the risk of acid reflux, but tea and alcohol, often thought to be culprits, seem to have little impact, finds a large study in Gut.
Acid reflux, also known as gastro-oesophageal reflux, is common and one of the most frequent causes of indigestion. Symptoms arise when stomach acid flows back into the oesophagus or gullet - often as far as the mouth - usually as a result of a weakened muscle at the bottom of the gullet. Typical symptoms include heartburn, excessive belching, and even respiratory problems.
The research team based their work on 47,556 people, who had taken part in two major public health surveys in Nord-Trondelag, a county in Norway.
The first survey, involving more than 74,000 people, was conducted between 1984 and 1986; the second spanned the period 1995 to 1997 and included more than 65,000 people.
In the second survey, 3153 people who complained of severe heartburn and reflux into the mouth within the preceding 12 months were identified as having acid reflux. Their average age was 52.
They were quizzed about their lifestyles, including diet, exercise, alcohol intake, and tobacco habit. And their responses were compared with those from 40,210 people without symptoms, whose average age was 48.
Lifestyle was strongly linked to acid reflux symptoms. People who had smoked every day for more than 20 years were 70% more likely to have acid reflux than non-smokers.
Salt intake proved to be as great a risk factor. Those who routinely added salt to meals were also 70% more likely to have acid reflux than those who did not. And those who ate salted meat or fish three or more times a week were 50% more likely to have acid reflux than those who never ate these foods.
Some lifestyle factors seemed to confer protection. Regular consumption of high fibre brown bread and 30 minutes of strenuous exercise at least once a week both halved the risk of developing acid reflux.
The explanation for dietary fibre might lie in the fact that it mops up large amounts of nitric oxide in the stomach, produced from nitrites in the diet, say the authors. Nitric oxide relaxes the muscle at the bottom of the gullet, so promoting reflux.
Surprisingly, heavy coffee drinkers (around 7 cups a day) were also around 40% less likely to develop acid reflux than those who drank one or fewer cups a day. However, the authors point out that people with acid reflux might abstain from coffee drinking, which could potentially skew the results.
But neither tea nor alcohol, irrespective of the quantities drunk, had any impact on risk.
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