Fridges blamed for Crohn's disease rise
Scientists say the link is due to food bugs that survive in cold temperatures and have been associated with the inflammatory bowel condition.
The fact Crohn?s emerged in the second half of the 20th century just as domestic refrigerators became widely available is no coincidence, they argue in The Lancet medical journal.
Dr Jean-Pierre Hugot, from the Robert Debre Hospital in Paris, who led the study, said today: ?All findings point to refrigeration as a potential risk factor for Crohn?s disease.?
Crohn?s is thought to be primarily an autoimmune disorder, but its cause is still unknown. Both environmental and genetic factors are thought to be involved.
Symptoms include pain, diarrhoea, fatigue and loss of weight.
The row over the measles, mumps, rubella (MMR) vaccine focused on Crohn?s disease as well as autism.
A possible link with measles led to suggestions that the vaccine may have contributed to a sharp rise in the number of children diagnosed with Crohn?s disease. However, this has largely been discredited.
Dr Hugot?s team examined the ?cold chain hypothesis? which suggests that certain bacteria such as Yersinia and Listeria ? commonly found in beef, pork, chicken, sausages, hamburgers, cheese and lettuce ? contribute to the disease.
These bugs can thrive in cold temperatures and contaminate refrigerated food.
The theory is that food left in people?s fridges, or stored on supermarket cold shelves, can be contaminated. Once in the gut, the bugs trigger an excessive immune response which in some individuals may set off an inflammatory disorder.
Domestic refrigeration began with the advent of ice containers in the 19th century, said the researchers.
The first true refrigerator was developed by Kelvinator in the United States in 1918.
It quickly caught on, and between 1921 and 1935, the annual production rate rose from 5,000 machines to 1,700,000. By 1937, nearly half of all Americans had a refrigerator.
In the 1930s, only wealthy families in Europe had fridges, and it was not until after the Second World War that ownership became more common.
Even in 1958, only 10% of French and 12% of British homes had a refrigerator, while ownership was as low as 2% in Spain, the Soviet Union and Japan.
The European exception was Sweden, where at the end of the 1950s just over half of families had an Electrolux refrigerator.
Population-based data indicate that Crohn?s prevalence began to increase in the 1940s or before in the US, in the 1950s or earlier in Sweden, in the 1960s in Britain, and later in southern Europe.
The trends showed ?temporal and geographical coincidences between the development of the refrigerator and the outbreak of Crohn?s disease?, said the scientists.
They pointed out that the refrigerator was only the end of the ?cold chain?. During its production and storage before being sold, a large proportion of food was kept at low temperatures.
Bugs capable of surviving the cold were known as ?psychrotrophic bacteria?. They thrived best at temperatures above 30C, but were able to grow more slowly in conditions of minus one to 10 degrees Centigrade ? precisely the range found in fridges.
Harmful psychrotrophic bugs included Listeria monocytogenes, Yersinia enterocolitica, Clostridium botulinum, and Bacillus cereus.
Yersinia and Listeria had both been discovered in Crohn?s patients using different testing methods.
More evidence pointing to Yersinia involved mutations in an immunity gene called CARD15 which are known to predispose people to Crohn?s.
It was thought that people with the mutations may be particularly susceptible to a biochemical effect of Yersinia.
Another clue was that the mutations emerged in the Middle Ages during outbreaks of the Plague.
The disease was caused by Yersinia pestis, a relative of the common food bug.
One possibility was that carriers of the mutation had a selective advantage against Plague, and met it with a more intense immune reaction.
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