Vitamin deficiency asthma 'link'
 Asthma affects 5m people in the UK |
A low intake of vitamins A and C could raise the risk of asthma, a team which reviewed 40 studies carried out over the past 30 years has said.
A Nottingham University-led team found people with a low intake of vitamin C had a 12% increased risk of asthma, the Thorax journal reported.
For vitamin A the raised risk was less clear cut, the team said, but there was still a significant association.
Asthma UK and the Medical Research Council said more research was needed.
There has been a lot of confusion over the link between vitamins and the condition, which affects five million people in the UK.
 |  The jury is still out as to how exactly vitamin intake and asthma are related  Leanne Male Asthma UK |
Previous studies have come up with a variety of conclusions.
In this study, the researchers analysed the relevant reports on both children and adults published since 1980.
They found no link for vitamin E, but said the associations for A and C were significant.
They concluded low levels of vitamin C - found in fruit and vegetables - increased the risk of asthma by 12%.
They were unable to put an exact figure on vitamin A - found in cheese, eggs and oily fish - but noted that those with severe asthma consumed on average half of the recommended intake of the vitamin.
Lead researcher Dr Jo Leonardi-Bee said: "Our findings indicate that low levels of vitamin C intake and to a lesser extent vitamin A are consistently associated with asthma risk to a degree that, if causal, would be sufficient to be clinically relevant."
He said it was now important to carry out larger-scale studies to clarify the link and to see if there was a direct cause between vitamin intake and asthma.
Other factors
Experts agreed more research was needed, but warned other factors would also play a significant role.
Glenys Jones, a nutritionist with the Medical Research Council, said: "The data provided is interesting, but inconclusive.
"There are many factors such as smoking, physical activity and socio-economic status that have not been taken into account.
"Therefore more research is required to investigate a causal relationship."
Leanne Male, assistant director of research at Asthma UK, added: "The jury is still out as to how exactly vitamin intake and asthma are related."
