Does drinking milk make phlegm? Do dairy products tend to worsen or prolong a cough? Despite all the claims there appears to be little research support these claims. It appears that only some people may be susceptible, and it only applies for a specific type of milk.
Recent research has shown that dairy products, especially milk, does not increase phlegm in the throat nose or chest nor does it increase the viscosity of phlegm making a cough worse or prolonging the time it takes to get over the cough. In one study subjects were exposed to cold virus and when they developed head colds their tissues were weighed. No significant differences were found between the amount of mucus produced by the group who drank milk and the group who did not.
The researchers said that certain dairy products are known to cause the reflux of acid from the stomach. This could trigger vocal difficulties and perhaps coughing bouts but there was no evidence that this was caused by increased phlegm.
Various people may also develop allergies to dairy products and this could also induce coughing. But there was no evidence of any direct, general effect of dairy products inducing an increase in mucus production.
However many people have disputed these claims and have had their cold symptoms improve (including asthma) when dairy is eliminated from their diet.
There is limited medical evidence showing that a substance derived from the breakdown of certain types of milk called A1 milk (see below)( beta-CM-7). This substance stimulates mucus production from glands in the gut.
It is possible that the same substance release from the bloodstream could stimulate the production and secretion of mucus production from respiratory glands. Further it has been suggested that not everyone is susceptible and that not all milk is the same.
Only some types of milk, from certain breeds of cow, lead to the production of the protein called beta-CM-7. This may explain the varying response in different groups of people.
To produce the effect the person has to be consuming the type of milk that contains beta-CM-7 and it must pass into the systemic circulation and the tissues have to be actively inflamed in order to stimulate the mucus production. Further research is needed to confirm this hypothesis.
One of the proteins in milk is called casein, and one of those is the beta casein. There are two major types of beta casein - Type A1 and A2.
A2 is generally regarded as a good natural protein, whereas the A1 protein is regarded as a mutant type. A2 is found in most of the traditional farm cows like Guernsey, Brown Swiss, and Jersey. The most popular cow in America, the Holstein, is however predominantly A1.
There are claims of an association between A1 beta casein in milk and increased risk of heart disease and diabetes, and is also associated with neurological disorders such as autism and schizophrenia. Hence all the controversy. Perhaps the mucus claim is another one of these.