Young children who regularly eat products containing milk fat are less likely to develop asthma, research suggests.
Milk is high in fats
Scientists say the finding provides strong evidence that while asthma may, in part, be a genetic condition, it is certainly influenced by lifestyle factors too.
A team from the Dutch National Institute of Public Health and the Environment analysed the diet of nearly 3,000 two-year-olds.
They found that by the age of three, those who had eaten full cream milk and butter on a daily basis were less likely to have developed symptoms of asthma.
Daily consumption of brown bread was also associated with lower rates of asthma.
The researchers, led by Dr Alet Wijga, say various components of milk fat - such as specific types of fatty acids, or other micronutrients - may help to protect against asthma.
It is now clear that there must be something in our modern western lifestyle that increases the risk to develop asthma.
Several experts have suggested that the increase in rates of asthma - and related conditions such as eczema - may be in some way related to a reduction in consumption of saturated fat, which is found in high concentration in milk.
And previous research has found a diet high in polyunsaturated fats - found in many margarines and vegetable oils - may double a child's chances of having asthma.
Dr Wijga told BBC News Online: "We think that the role of fatty acids may be important. The fat we eat consists of a variety of different fatty acids, depending, among other things, on whether the fat is derived from plants, from mammals or from fish.
"The balance between these different types of fat in the diet influences the working of our immune system.
"The increase in the prevalence of asthma, eczema and hay fever in the western world may be related to the reduction in the consumption of saturated fat and the increase in the consumption of n-6 polyunsaturated fatty acids and in particular linoleic acid. Our findings are in line with this hypothesis."
Dr Wijga said it would be wrong at this stage to recommend young child eat a diet high in saturated fats, as there was significant evidence that this was bad for cardiovascular health.
The increasing prevalence of asthma almost certainly reflects multiple lifestyle changes over the last three decades
Professor Martyn Partridge
However, she said: "I could imagine that, in the future, we will find that nutritional advice needs to be more specifically directed at different age groups.
"Nearly all the evidence on the harmful effects of a high consumption of saturated fat has been collected in adults and we know little about the risks and benefits of fat consumption in pre-school children."
Dr John Harvey, of the British Thoracic Society, said more research was needed.
"Evidence already shows that mothers who breastfeed reduce the risk of their child having asthma symptoms.
"Moderation is the key, however, since butter and cream need to be controlled and eaten as part of a healthy balanced diet, also rich in fruit and vegetables - this has also been shown to be important in improving lung function.
"In addition some children may be allergic to dairy products. If parents are in any doubt they should contact their GP."
Professor Martyn Partridge, chief medical adviser to the National Asthma Campaign, said: "The increasing prevalence of asthma almost certainly reflects multiple lifestyle changes over the last three decades.
"Nutrition may be one such change but there is too little data yet to permit concrete dietary advice to be given as to how to eat to avoid asthma."
The research is published in the journal Thorax.