Milk is secreted by the mammary glands (breasts) of all female mammals and marsupials in order to feed their young. It contains nutrients such as protein, fats, carbohydrates, vitamins and minerals that are ideal for the young of each species.
Dairy products are a staple food in the diet of nearly every civilisation around the world, either in its original liquid form or as cheese, butter, yoghurt, cream, or in many other forms. The intake varies from one place to another. The Japanese have relatively little, Europeans quite a lot, and some Arab tribes live almost entirely on dairy products. Milk is an excellent source of carbohydrates, protein and fat, and the sugar lactose.
Man can virtually live on milk alone if necessary. Some specialised dairy products, such as yoghurt and junket, are excellent aids to digestion and bowel function. Cheeses are compressed energy, and are included in survival rations.
As with all foods, too much can be harmful. Those who have a high cholesterol level in their bloodstream and the more obese members of the community should not eat whole milk products, but skim milk and fat reduced dairy products can still be consumed. The theory that milk increases mucus production in the nose and throat is a myth. There is no benefit in stopping dairy products to ease mucus congestion.