Milk is a poor source of copper--a nutrient which is known to be limiting or marginal in many western diets. Lactose (a major nutritional constituent of milk) may interfere with copper utilization in milk and in the overall diet. It is postulated that the strong association between the consumption of milk and dairy products (especially fresh milk and non-fermented milk products) and the incidence of ischaemic heart disease (IHD) indicates a central role for a dietary copper deficiency in the aetiology of this disease.