This study is based on a large representative population sample of middle‐aged men.
The definition of the metabolic syndrome that we have used is relatively close to that proposed by the World Health Organization.15
This and many other definitions use specific levels of blood pressure, lipids, blood glucose etc, each of which is defined in original units. This ignores differences between laboratories, and such differences can be large. Although the use of criteria in terms of “the top 10%” of a variate ignores differences between populations, we believe that such differences are likely to be relatively small. In any case, the fundamental difficulties with the whole concept of the syndrome raise more important questions than small differences in diagnostic criteria.
Because of the differences between studies in diagnostic criteria and in age distribution, comparisons of the prevalence in these older men in Caerphilly with those reported in other studies are not very meaningful. Most studies, however, yield prevalence estimates for the syndrome that are somewhat higher than the present estimates, generally around 20–30%.6,14,16
The clinical importance of the syndrome in our cohort is indicated by the significantly increased risk of subsequent ischaemic heart disease events, death and diabetes (RR 4.09, 2.92 and 5.74, respectively). These estimates are similar to those reported from other studies.3,4,6
The syndrome has been much criticised,5,6,7
and the fact that the prediction of disease show a very marked increase with increasing numbers of the criteria that are used in the definition of the syndrome, indicates that the choice of the two or more criteria is very arbitrary indeed. Furthermore, prediction of disease events by the separate criteria differs enormously, and, in the present data, the top 10% of men defined by body mass index alone had no significantly increased risk of a disease event, although, the insulin/glucose criterion was a significant predictor of all the disease events, including stroke. Thus, giving equal weight to various criteria is unreasonable.
The prevalence of the syndrome is markedly associated with the consumption of milk, and this is apparent both in men grouped by their own estimates of milk consumption, and in those grouped by milk intake data obtained from the 7‐day weighed intake records. Furthermore, estimates of total dairy food consumption (milk, cheese, cream, butter and yoghurt) made from the weighed records kept by 603 men show a decreasing prevalence of the syndrome with increasing dairy consumption, the adjusted RR in the quarter of men with the highest dairy intakes being 0.44 (0.21 to 0.91). Although these results could be explained by confounding, it seems most unlikely that a factor or factors further to those for which adjustments have been made could explain, let alone reverse, the trends observed.
Furthermore, a number of other studies show this same negative association with milk consumption. In the Terhan Lipid and Glucose Study of 827 subjects,9
a number of factors were found to be associated favourably with dairy consumption, including the metabolic syndrome (OR 0.69; p<0.02). In the Women's Health Study of 10
066 US women,10
the adjusted OR for the syndrome in the one‐fifth of the women with the highest total calcium intake was 0.66. In the DESIR study of 4976 subjects in France,17
men who took more than one portion of dairy produce per day had an OR for the syndrome of 0.61 (0.41 to 0.90), although in women an OR of 0.76 (0.48 to 2.56) was not significant.
The CARDIA study8
is of particular interest, being prospective over 10 years in subjects aged 18–30 years. A negative association between milk consumption and the development of the syndrome was found, but only in 909 subjects (30% of the total cohort) who had been overweight at baseline. In this subgroup, the risk of the syndrome was 0.28 (0.14 to 0.58) in those with the highest dairy food intake, relative to the risk in those with the lowest dairy intake. The authors estimated that each additional daily serving of dairy foods was associated with a 21% lower odds of the development of the syndrome.
In contrast to all these are the results from 4000 women aged 60–79 years in the British Women's Heart and Health Study;18
111 women (2.8% of the total cohort) who reported that they never drank milk had an adjusted OR for the metabolic syndrome, relative to 3913 women who drank milk, of 0.55 (0.33 to 0.94). Women who drink no milk are, however, unusual. A high proportion is likely to be lactose intolerant, and such a group is unlikely to be representative of the general population.
The prediction of diabetes by milk drinking is only suggested in the present data (table 5). Neither the trend nor the relative odds in the men with the highest milk intake (0.57) is significant, nor are the odds significant when based on the consumption of all dairy foods (0.74, (0.26 to 2.05) in men with the highest dairy consumption). In a much larger study, however,19
a significant protective effect of dairy food consumption was shown, the adjusted RR in the one‐fifth of the women with the highest intake being 0.79 (0.67 to 0.94). These authors estimated that each daily serving of dairy foods was associated with a 4% lower risk of developing diabetes.
Elsewhere, an overview of 10 major prospective studies has demonstrated a negative relationship between milk consumption and both incident ischaemic stroke and ischaemic heart disease.20
The present data add further to the evidence that milk and dairy products “fit well into a healthy eating pattern”.21
What this paper adds
- Further evidence of benefit from milk and dairy foods, against a background of widespread uncertainties about the benefits of these foods
- Criticisms of the so‐called “metabolic syndrome”, further to those already published
Milk consumption has fallen markedly in the UK during the past 25 years. This paper adds to the evidence that milk and dairy products fit well into a healthy eating pattern and that their consumption should be promoted