Ideally, the relationship between dairy foods and health would be measured by very large, very long-term intervention trials. In practice, however, the best available data are often from large, long-term observational studies. While not able to prove a cause and effect relationship, such prospective cohort studies and other types of observational data provide a ‘real life’ picture of a food in the diet and in a particular dietary pattern.
A number of analyses have pooled data from individual intervention or observational studies and the combined results increase statistical power and add weight to the results of single studies. Such meta-analyses provide the most robust evidence of the relationship between milk and dairy foods and health and, along with the recent reviews (both systematic and narrative), are discussed here. However, some individual studies conducted in European populations are also highlighted. These give an indication of the potential health effects of milk and dairy foods in relation to the particular amounts, types and patterns of consumption in Europe.
Intakes in European countries may be different to other parts of the world such as the United States or Asia where dairy consumption is often lower; they can also differ between European countries. In addition, the composition of milk and dairy products can vary between Europe and elsewhere depending, for instance, on animal feeding practices e.g. whether the cows are fed predominately on grain or are on fresh pasture. Fortification practices can also differ e.g. vitamin D is routinely added to milk in the USA, and it is mandatory to do so in Canada. This is the case for low-fat milk in some Scandinavian countries including Norway but, on the whole, consumption of vitamin D-enriched milk is less common place in other parts of Europe. All of these factors may influence the results of research on the impact of dairy on health, and help explain differences between Europe and other parts of the world, and also within Europe.