Traditionally milk has been regarded as important with respect to nutrition because it is a source of calcium and several vitamins. However liquid milk consumption has suffered because of the competition other beverages such as sugar sweetened soft drinks and various forms of bottled water. In addition milk and/or milk products contain saturated fat, which according to the official dietary advice should only be consumed in limited quantity. As a consequence the fat is often removed to produce “low fat” versions. In many of these products the fat has been replaced by sugar. It is extremely difficult to relate milk and or individual milk products to any aspect of health or disease. Epidemiological studies which monitor what different populations consume and attempt to relate to the incidence or death rate of a specific disease are subject to all sorts of errors and misinterpretations. How reliable is the information collected on the dietary patterns? Even if this information is reasonably accurate can we be sure it is representative of the whole population being studied? Are diagnoses of diseases accurate? Even the causes of death shown on death certificates are notoriously unreliable. The famous Seven Countries Study which is the basis of the relationships between saturated fat (SFA), cholesterol in blood (TC) and the death rates due to Coronary Heart Disease(CHD) has been totally discredited because the conclusions are based on results from a restricted number of selected countries. When data are included from many more countries any relationships disappear. If the original findings were actually genuine it would simply have demonstrated an association which does not necessarily mean that there is a cause and effect. To draw an analogy there may well be an association between the number of police observed on the streets and the level of crime. This does not mean the high visibility of police is the cause of the high crime rate and it certainly does not follow that reducing the police will reduce the crime. Unfortunately this is the rationale which underpins all the concern about TC!
A number of investigations have studied the relationship between milk/milk products and various indicators of conditions of ill-health. A comparison of the effects of high and low intakes of dairy products with a calorie-restricted diet was made in healthy men and women aged between 18 and 60 years. All of them were classified as obese (they had a BMI above 30) at the outset. Although there were 41 participants initially, 9 of them dropped out. Both groups lost weight, the results showed that those who had the high intake of dairy lost considerably more weight than those on a low intake. With respect to glucose tolerance there was a significant improvement in the high dairy group but no change in those with a low dairy intake (1).
In a meta-analysis based on 6 studies it was found that those with the highest dairy consumption had a reduction of 13% in all-cause mortality compared with those who had the lowest consumption (2). With heart disease an analysis based on 9 separate studies also found a small reduction in death rate for those with a high intake of milk and milk products. For both ischaemic and haemorrhagic strokes the death rates were reduced in those with the highest dairy consumption. There were 5 different studies on the relationship between dairy consumption and diabetes: all of them found that there was a reduction in the incidence with a relatively high intake of milk and milk products. In the light of the totality of these results the authors commented that:
“The similarity of the estimates of risk is remarkable and, although conclusions have to be tentative, it seems not unreasonable to conclude that there is no evidence that dairy foods as a total group are associated with harm to health either in terms of death, heart disease, stroke or diabetes, but are probably beneficial in relation to these disease outcomes.”
REFERENCES
- M B Zemel (2004) Obesity Research 12 (4) pp58-590
- P C Elwood et al(2010) Lipids 45 pp925-939