Vegetables rich in nitrates boost stomach lining, thanks to friendly mouth bacteria
Vegetables rich in nitrates, such as spinach, may help to protect against stomach ulcers thanks to bacteria in the mouth, a Swedish study suggests. The work challenges earlier suggestions that a diet rich in nitrates could pose a health risk.
Joel Petersson was awarded his PhD by the University of Uppsala on May 9 for the study, which shows that rats fed on a nitrate-rich diet had a thicker layer of mucus lining their stomachs, protecting them from hydrochloric acid in gastric juice and cutting the risk of ulcers.
Petersson found that mouth bacteria play a vital part in the process. Nitrates in food are absorbed in the gut and enter the blood stream. From here they get into saliva but are reduced to nitrites by oral bacteria. After being swallowed, the nitrites are reduced to nitric oxide by stomach acid. Nitric oxide, an important signalling molecule, triggers an increase in the flow of blood to the stomach, helping to renew and thicken its mucus lining.
When Petersson gave rats an antibacterial mouthwash to kill the oral bacteria, he found they were more vulnerable to stomach ulcers. He suggests that people using these mouthwashes regularly may be at risk, especially if they are also frequent users of nonsteroidal pain killers like aspirin which can also damage the stomach lining. ’There are other much safer ways of blocking the production of the sulphur-containing compounds in the mouth if you have bad breath,’ he said.
Between 60 and 80 per cent of the nitrates consumed in a normal Western diet come from vegetables, with beetroot, celery and spinach containing particularly high-levels of 1-3g per kilo.
Studies in the 1970s suggested a link between high nitrate levels in drinking water and both stomach cancer and the rare blood condition in babies, methaemoglobinaemia. ’We have since wasted millions in trying to reduce nitrate levels in drinking water when there is no real evidence to show that it is harmful to humans. If you do eat a lot of nitrate it is very easy dealt with - you just pee it out,’ Petersson said.
Nigel ’Ben’ Benjamin, now a consultant in acute medicine at the Peninsula Medical School in Plymouth, UK, discovered a different protective mechanism for nitrates in the 1990s. He showed that the combination of nitric oxide and acid controlled the growth of dangerous bacteria like salmonella in the gut. ’The Swedish study has shown this further effect in animals and I would certainly expect the same mechanism to exist in the human stomach,’ said Benjamin. ’This is exciting work and gives us further reasons for eating a diet that contains lots of fresh vegetables.’
et alAm. J. Physiol. Gastrointest. Liver Physiol.292et alJ. Clin. Invest.113, 106 (DOI: 10.1172/JCI19019)