This study presents estimates of the cross-sectional relationship between overweight and obesity and several chronic conditions and diseases in a representative sample of German adults. The prevalence of overweight and obesity increased with increasing age and the percentage of men and women with abdominal obesity rose steadily with age in overweight and even in the normal weight persons, as defined by BMI.
The prevalence of the majority of chronic conditions and diseases rose with increasing BMI. Both overweight and obesity in men and women were significantly associated with cardiometabolic risk factors and osteoarthritis, which is consistent with findings from the representative telephone survey (Behavioral Risk Factor Surveillance System, BRFSS) in the United States among adults aged 18 years and older . This cross-sectional study showed a strong association between overweight and obesity, and cardiometabolic risk factors such as high blood pressure, high cholesterol, and arthritis. Several large cohort studies also found a direct positive association between high BMI and hypertension [6, 39], and increased BMI and osteoarthritis . A systematic review and meta-analysis of prospective cohort studies on comorbidity related to obesity and overweight demonstrated a significant association between overweight and obesity with incident diabetes, CVD, asthma, gallbladder disease, osteoarthritis, and various types of cancer . Furthermore, our survey results indicated a positive association among men and women between overweight and obesity and diabetes and gallbladder disease, which is also consistent with findings from large cohort studies [8, 9, 19, 20]. However, in our study, the relationship between overweight and obesity and diabetes and gallbladder disease was only significant among women. The stronger association between obesity and gallbladder disease has been observed in other studies, but the reason still remains unclear [41, 42]. The missing significance between overweight and obesity and diabetes among men may be due to the lower prevalence of diagnosed diabetes in men compared to women. The diabetes diagnosis in our study based on a self-reported physician diagnosis and the current drug use without any blood glucose analyses. In Germany, the prevalence of undiagnosed diabetes is higher among men than among women [43, 44]. Therefore, the true association between overweight and obesity and diabetes in men could be underestimated.
The increased risk for CVD among overweight and obese has been investigated in several prospective studies. In the Framingham Heart Study, a prospective cohort study with 44 years of follow-up, both men and women with overweight had a two-fold higher, obese men had a 1.46 times higher (95%-CI: 1.20-1.77) and obese women a 1.64 times (1.37-1.98) higher risk for CVD . A meta-analysis of cohort studies including more than 300.000 persons indicated a 30% higher risk for CHD in overweight and an 80% higher risk in obese men and women . However, in our study the association between overweight and CVD were neither significant in men nor in women, and for obesity and CVD we only observed a significant higher risk in men. The missing significance among women could be due to gender disparities in the diagnosis of the underlying diseases in the CVD group, in particular CHD. In fact, analyses by subgroups confirmed that the observed sex difference is related to CHD. More than a decade ago, when this survey was conducted, the diagnosis of CHD was a typical male diagnosis and not very commonly diagnosed among women . Heart failure is a weak diagnosis compared to other disease endpoints, and should be interpreted with caution. The diagnosis stroke is probably under diagnosed in a national health survey, as participants with serious diseases and disabilities would not have participated.
Regarding obesity and allergic diseases the published literature is controversial and the reasons for inconsistent study results remain unclear. Two non-representative cross-sectional studies found an independent effect of overweight on atopic diseases only among women, but not among men. The Humboldt Study 2003 collected data from around 2000 18-79 year old Canadians  and Kilpeläinen et al. 2006 included 10667 Finish students aged 18-25 years . In contrast, representative data from the NHANES Survey 2005-2006 indicate that obesity was not independently associated with atopy . Nevertheless, our study indicated a significant inverse association between abdominal obesity and atopic disease in women and overweight and obesity and atopy in men. The differences between study findings might be due to different underlying diagnosis criteria. In the Humboldt Study 2003 allergic diseases were assessed by a questionnaire and skin prick test  and NHANES used a positive immune essay test result to define atopy . The cross-sectional study with young Finns used a physician diagnosis of allergic rhinitis or allergic conjunctivitis and in our study participants were asked whether a physician had ever told them that they had an atopic disease (e.g. allergic rhinitis, allergic contact exzema, neurodermatitis, food allergy, urticaria). More research is needed to clarify the comparability of different diagnosis information.
As in the descriptive analyses of prevalence estimates across BMI categories, we did not observe an independent significant association of overweight and obesity with lower respiratory disease, upper GIT disease, and cirrhosis of the liver, thyroid disease, malignancy or mental health problem in the multivariate analysis.
In fact, after adjustment for BMI, abdominal obesity was associated with higher odds ratios for cardiometabolic risk factors, diabetes mellitus and gall bladder diseases, but the estimates did not show significance among men. This might be due to the use of WHO recommendations for the sex specific cut-offs for high risk WC (men: ≥102 cm; women: ≥88 cm) . Although results from a longitudinal cohort study showed that even WC values below these cut-offs are associated with increased risk of diabetes in men and women, it could be that the thresholds for men might be inappropriately set to detect significant associations between WC and cardiometabolic risk factors and diabetes mellitus . Furthermore, while men had larger mean values for WC compared to women the percentage of men with abdominal obesity is lower than among women. It seems that the used WC cut-off is a better predictor among women compared to men.
To our knowledge, the relationship between weight status and prevalence of different conditions and chronic diseases has not been described for the German population. These presented results are an important baseline investigation for further longitudinal analyses of upcoming representative data from the next survey. This survey includes participants of GNHIES and, therefore, will allow us to compare the obesity associated disease burden between two surveys at different time points (1997-1999 and 2008-2011) of the last decade.
Our study has several limitations. First, the presented data on comorbidity of overweight and obesity is restricted to the population 18 to 79 years. Thus, our results cannot be generalized to persons 80 years of age and older. Second, given the cross-sectional design, the results of the present study do not permit any conclusions on causality or causal directions between obesity and comorbidities. Third, the use of self-reports to identify chronic diseases can lead to recall and misclassification bias. Self-reports have been widely used in epidemiological studies to assess the burden of chronic diseases. For most conditions specificity of self-reported information is high, in particular if additional information on medication use is used for internal validation . In the present study, we considered medication use for hypertension, hyperlipidemia, hyperuricemia, diabetes, and thyroid disease. We cannot exclude, however, that we missed participants with undiagnosed or subclinical disease. For example, we only considered a physician-diagnosed “mental health problem” and did not use additional information based on the World Mental Health Composite Diagnostic Interview administered in a subset of the study population . We also did not consider the available blood pressure or serum lipid measurements, because objective measurements to define subclinical or previously undiagnosed disease were available for only some conditions. Finally, it is possible that selection and survivor bias contributed to underestimate the burden of comorbidity associated with overweight and obesity. In particular, men and women with serious conditions likely to cause irreversible organ damage, such as stroke or malignancy would be expected to be under-represented in this national survey.
In addition, BMI is a fairly blunt instrument through which to define overweight and obesity and does not adequately reflect body composition, especially unfavorable fat mass distribution. BMI does not discriminate between body fat mass and lean tissue mass and it is possible that we have underestimated the abdominal fatness in older individuals, who have higher percentages of fat in relation to lean muscle mass compared to younger men and women. Therefore, we analyzed WC as a marker for abdominal fat mass.
Despite these limitations the results of the present study are based on a large nationally representative sample of 18-79 year old adults in Germany and a selection bias can be neglected. Our cross-sectional results on comorbidity of overweight and obesity are in line with large prospective studies focusing on single health outcomes, and the above mentioned biases might not affect our results substantially.