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To report a negative association between milk or dairy consumption and the metabolic syndrome and to examine associations within the Caerphilly cohort.
A representative sample of men aged 45–59 years in Caerphilly, UK.
Data on fasting blood glucose and plasma insulin, fasting plasma triglycerides and high‐density lipoprotein cholesterol, body mass index, and blood pressure were used to define the metabolic syndrome in terms of levels of two or more variates within the top 10%. The clinical importance of the syndrome was assessed from 20‐year incidence of diabetes, vascular events and deaths. The relationships between the syndrome and the consumption of milk and dairy products was examined using data from both a semiquantitative food frequence questionnaire, and from a 7‐day weighed intake record which had been kept by a 1:3 subsample of the men.
There were 2375 men without diabetes in the cohort. The prevalence of the metabolic syndrome was 15%. Men with the syndrome had significantly increased risks of a subsequent ischaemic heart disease event, death or diabetes. Negative relationships were shown between both the consumption of milk and dairy produce, and the syndrome. Adjusted odds ratio in men who regularly drank a pint of milk or more daily was 0.38 (0.18 to 0.78) and that for dairy food consumption was 0.44 (0.21 to 0.91). Milk intake showed no significant trend with incident diabetes.
The consumption of milk and dairy products is associated with a markedly reduced prevalence of the metabolic syndrome, and these items therefore fit well into a healthy eating pattern.
The metabolic syndrome has been termed the deadly quartet, and has been said to be the fastest growing disease entity in the world.1 On the other hand, although it does predict vascular disease and diabetes quite powerfully,2,3,4 it is probably not a true syndrome and is best thought of as simply an elaborate risk formula.5,6,7
A number of reports have shown negative relationships between the syndrome and the consumption of milk or dairy food intake.8,9,10 Here, we report the prevalence of the syndrome in the Caerphilly cohort of middle‐aged men; its importance in terms of the prediction of diabetes, vascular disease events and death, and the relationship of the syndrome with the consumption of milk and dairy foods.
The Caerphilly Cohort Study was set up in 1979–83. It was based on 2512 men aged 45–59 years.11 Data were collected at baseline on items relevant to the identification of the metabolic syndrome. After exclusion of men with diabetes, men were judged to have the syndrome if they had two or more of the following criteria:
Food consumption was assessed at baseline from a semiquantitative food frequency questionnaire completed by all the men with help from their partner. This included the quantity of milk usually drunk each day. A representative 1:3 sample of the men also kept a 7‐day weighed dietary intake record.12 Nutrient intakes were calculated using appropriate food composition tables. The total intake of milk was recorded as all milk drunk and added to drinks, milk added to cereals, milk used in puddings and other recipes, together with dried milk converted to the equivalent weight of whole milk.
At 5‐year intervals, the men were re‐examined. Self‐reported diabetes was recorded and incident vascular events were identified.13,14 A diagnosis of ischaemic heart disease (ICD I21‐5, 10th revision) included deaths certified as due to ischaemic heart disease together with non‐fatal myocardial infarction. Ischaemic stroke (ICD I63‐4) was diagnosed according to accepted criteria. Follow‐up was continued for approximately 20 years.
After the exclusion of men with diabetes from the cohort, data are available for 2375 men. The numbers who fulfilled the separate criteria of the metabolic syndrome are shown in table 11.. Approximately 15% fulfilled the criteria set for the metabolic syndrome—namely, two or more of the separate criteria. Of the 640 sample of men who had kept a 7‐day weighed dietary record, did not have diabetes at baseline, and complete data were available for 603 men. Of these, 14% fulfilled the criteria for the syndrome.
In table 22,, the clinical importance of the syndrome is assessed. There were marked increases in incident disease events in men with the syndrome at baseline. For ischaemic heart disease, the adjusted risk ratio (RR) was 1.79 (95% CI 1.36 to 2.37) and for deaths from any cause, 1.46 (1.12 to 1.88). Prediction of incident diabetes was particularly strong, with a RR of 4.09 (2.92 to 5.74). While the RR of ischaemic stroke was increased, this was not significant.
Table 22 also shows incident disease events and deaths for numbers of the criteria other than the two or more which defines the syndrome. As expected, other than for stroke, there were enormously strong gradients in the risk with increase in the number of criteria fulfilled. This is particularly evident in the data for incident diabetes.
Table 33 shows a marked negative and significant relationship between milk consumption and the presence of the syndrome. In the total cohort, men who drank one pint of milk or more per day had an adjusted odds ratio (OR) for the syndrome of 0.38 (0.18 to 0.78) relative to men who stated that they drank little or no milk. Data for the men who had kept the 7‐day intake records show a closely similar effect, the odds of having the syndrome in the quarter of men with the highest milk intake relative to that in the quarter of men with the lowest intake being 0.43 (0.20 to 0.95).
Data from the 7‐day weighed dietary intake records enabled us to estimate the total calorie intake of each man from dairy foods, defined as milk, cheese and yoghurt. The adjusted relative odds for the occurrence of the syndrome in quarters of men defined by increasing consumption of dairy foods was 1.00; 0.48; 0.51 and that in the quarter of men with the highest dairy intake was 0.40 (0.20 to 0.79). The trend in these data is significant (table 44).). In fact, the association with dairy foods defined to also include butter and cream is almost identical (relative odds in the quarter of men with the highest intake 0.44 (0.21 to 0.91), p=0.023).
Finally, although the data are sparse, table 55 presents data for incident diabetes in relation to milk consumption at baseline. There is little suggestion of a trend (p=0.247), and neither the adjusted OR in the quarter of men with the highest intake of milk nor the highest consumption of dairy foods (not shown) are significant (0.57 (0.20 to 1.63) and 0.74 (0.26 to 2.05), respectively).
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 10066 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 55).). 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
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
The Caerphilly study was conducted by the former MRC Epidemiology Unit (South Wales) and was funded by the Medical Research Council of the UK. The archive is now maintained by the Department of Social Medicine in the University of Bristol, UK.
Funding: Funding for the Caerphilly Cohort Study was by the UK MRC. More recently, PCE and JEP have been supported by Cardiff University.
Competing interests: None.
Ethical approval: Every subject signed his agreement to the study at each (five year) phase of the Caerphilly Cohort Study, and ethical approval was granted for every (five year) phase of the work by local ethics committees—most recently by Gwent Ethics Committee.