Epidemiological research in primary care is, different from population-based samples, highly relevant when investigating topics related to physician – patient interaction. Primary care in Germany is characterized by a high patient load of about 73 consultations per day , which is much higher than in other countries in Europe and worldwide. Straight and easy to follow rules for screening and detection of cardiovascular disease are warranted to ensure, that busy clinical routine does not detract from cardiovascular prevention and chronic disease treatment. Obesity and in particular abdominal obesity has been recognized to be linked to an increase in cardiovascular risk and therefore the present analysis on the interrelationship of both measures and their relation to cardiovascular risk has been conducted.
The present analysis, based on data derived from more than 35,869 adult primary care attendees, uncovered several key aspects of overweight and obesity in primary care: 1) it documents a very high prevalence of overweight (36.5%) and obesity (23.9%) and of an increased and high WC in primary care practice in 2005, 2) it shows that a high waist circumference identifies patients with an increased cardiovascular risk even within the normal weight, overweight and obese patient group, 3) it confirms a tight relationship between waist circumference and an increase in cardiovascular risk and 4) it highlights a remarkable risk increase with BMI, WC and the combination of both measures.
Prevalence of (abdominal) obesity in adults seeking primary care
Although difficult to compare with other studies due to considerable a difference in methods and sampling the present data indicate a high prevalence of overweight and obesity in primary health care in Germany. According to the "Shape of the Nations survey" 39% of all people visiting a primary care physicians worldwide were overweight or obese; in North America, this proportion was 49% . In the Netherlands, a population closely resembling the German population, obesity was observed in 8.9% of men and 12.4% of women; for overweight these percentages were 42.2% and 30.4%, respectively . On the other hand, in primary care of the southeastern United States (1999–2002) substantially higher prevalence rates for overweight (white women 26%, men 24%) and obesity (white women 36%, men 32%) have been reported . Previous data from German primary care are available for 2001 from the HYDRA- and for 2003 from the DETECT-study [4, 20]. Prevalence rates in 2001 were 37.9% for overweight and 19.4% for obesity, prevalence rates in 2003 were 37.3% for overweight and 22.5% for obesity.
36.4% of male and 41.5% of female patients in our primary care cohort had a high WC (> 102 cm men, > 88 cm women). This appears high as compared to population-based samples across Europe [21–26], which one would expect based on the higher morbidity in a primary care sample. It is lower, however, as compared to the recent nationwide DETECT study of 55,518 consecutive German primary care attendees. In this survey, 43% of male and 53% of female patients met criteria for abdominal obesity (waist circumference ≥ 102 for men and ≥ 88 for women) . Methodological differences between the GEMCAS and the DETECT cohort may account for differences in prevalence rates reported. For example, GEMCAS excluded physicians specialized in diabetology or cardiology in an attempt to document prevalence rates in a broad sample of primary care attendees not being confounded by a large group of multimorbid patients attending a specialized physician. Secondary to this, the difference may be related to the fact that more diabetic patients were included in DETECT (14.6% vs. 12.4%) and patients were slightly older 53.9 vs. 51.7 years. Data from another source became recently available from the global IDEA study in primary care in 63 countries [27, 28]. The data show a fairly consistent prevalence of overweight all over the world with substantial differences in obesity prevalence. Whether this observation could also be due to different BMI thresholds that may apply in particularly Asian countries is a matter of debate.
Waist circumference in the overweight
There is some confusion both from the physician and patient perspective as to being overweight measured by BMI indicates an increased cardiovascular risk. A modest elevation of BMI may be simply due to a higher muscle mass, at least in younger male patients. We were therefore interested to assess if and to what extent WC is suitable to discriminate between normal and elevated risk. The data from the present study clearly show that even in the subgroup of overweight as well as in the subgroup of normal weight patients there is a proportion of patients with an elevation of waist circumference and an unfavourable cardiovascular risk profile. This could guide both physicians and patients towards more aggressively lowering increased body fat in high risk patients with overweight also.
Earlier studies have focussed on whether BMI, abdominal obesity or measures like waist-to-height ratio (WHtR) or waist-to-hip ratio (WHR) may be best to describe an excess of fat and its relation to cardiovascular risk . Several studies have described that WC is a better predictor of cardiovascular risk outcome than BMI [5–8]. While this debate is very valid, the mostly used measure of obesity in primary care is still BMI for which both components (weight, height) are easy and not offensive to determine. Given this standard, it is reassuring to know that normal-weight patients generally have a normal WC and a normal cardiovascular risk. On the other hand, obese persons have a high WC and a high cardiovascular risk. For the group of patients in between, however, it is necessary to measure WC to determine body fat distribution, since 31% of male and 54% of female patients have a high WC when in the overweight category by BMI. As shown in Table 2 & 3 most risk factors are significantly elevated in overweight patients with a high WC, the high cut point showing the highest PRRs (stratified into age group and gender). Tables 4 and 5 nicely illustrate that it is particularly hazardous to have a low to moderate BMI but a high degree of abdominal obesity. A higher BMI with a low waist circumference on the other hand may point at individuals with either a more favourable fat distribution or a higher muscle mass (particularly in overweight male patients).
Strength and limitations
Despite the strengths of the study (sample size, representativeness for patients in primary care, simultaneous coverage of structural, doctors and patients perspective) two limitations need to be highlighted: While the data set is representative for the primary care population it may be less so for the general population. The degree of representativeness of the GEMCAS sample for primary care has been reported in more detail by Moebus et al. . In short, 2,600 out of the 17,271 initially contacted primary health care practices responded to the invitation to participate in the study (15% response). The response rate varied slightly in the different postal code areas but no differences greater than ± 2% between contacted and participating sites for each region could be observed. The first 2,070 response faxes were collected and analyzed for eligibility. These revealed 1,835 eligible physicians out of which the first 1,700 were recruited for participation. Among these, 140 cancelled their participation before starting the study, mainly due to time-related issues, communication problems or illness. 33 of the 1,835 originally eligible physicians were recruited in a second run to replace cancellations among the 1,700. The second limitation was that the Body Mass Index was self-reported in 2/3rd of the patients in GEMCAS. This may indicate, that the prevalences reported are likely lower bound estimates for the true prevalence in this population .