The World Health Organization [1
] rates obesity as the 5th leading global risk factor for mortality in the world with 2.8 million deaths (4.8% of global death) and 10th for global burden of disease. With regard to mortality, the results of a recent report that used data derived from 19 prospective studies with 1.46 million white adults and a wide range of body mass index (BMI) were impressive: they showed that hazard ratios for all-cause mortality was up to 2.51 in patients with BMI higher than 40
kg/m² and was 4.42 for deaths due to cardiovascular diseases in the same group of subjects, also restricted to healthy participants who never smoked [2
However, obesity cannot only be seen as a risk factor for mortality. It is in fact a chronic disease that produces an increase in morbidity and dependence on others for daily needs and is responsible for the loss of healthy life years, estimated in 2.3% of disability-adjusted life years (DALYs) [1
]. Obesity as an impact of patients' live as it affects disability-free life by reducing it to 2.7 years in men and 3.6 years in women and, at the same time, by increasing the whole duration of disability to 2.0 years in men and 3.2 years in women [3
] meaning that obesity-related disability increased in conjunction with declining mortality rates. Recently, the National Health and Nutrition Examination Surveys (NHANESs) analyzed data from two periods (1988–1994 and 1999–2004) [4
]. Results show that, compared to normal-weight subjects, persons with mild obesity had twice the odds of daily life activities (ADLs) limitations (OR: 2.11; 95% CI: 1.15–3.86), while those with severe obesity had four times (OR: 3.96; 95% CI: 1.79–8.79). Furthermore, between NHANES I and NHANES II, the OR for obese persons, compared to normal-weight subjects, increased by a factor of 1.56 between time 1 and time 2 (95% CI: 1.03–2.36) therefore, a prolonged duration of obesity determined an further increase in the likelihood of having limitations in ADLs.
The most relevant issues responsible for health deterioration in obese subjects, and their connection to obesity degree and age, are not completely clear yet [5
]. The results of a European population study (SHARE: Survey of Health, Ageing and Retirement in Europe) were reported in a paper describing the health correlates of obese subjects aged 50 years and over [6
]. Results showed that, compared to normal-weight subjects, obese persons had between 2 and 2.4 the odds of reporting health complaints, between 2.4 and 2.7 the odds of reporting two or more chronic diseases, and between 0.4 and 0.5 the odds of self-reporting good to excellent health. In addition to this, obese men also reported between 1.6 and 2.4 the odds of having a physical disability, while women reported even more disability, as they reported between 2.1 and 3.5 the odds of physical disability compared to nonobese women.
It is likely to suppose that the increase of musculoskeletal and joint problems and the association with other chronic diseases might explain mobility limitations (e.g., bathing, dressing, getting in or out of bed, walking, climbing stairs, raising from a chair), early fatigue, dyspnoeas, and a reduction in different kinds of job tasks [7
]. The issue of mobility limitations is one of the most studied: a recent literature review evidenced a clear relationship between increasing obesity severity and reduced mobility, both in cross-sectional and longitudinal perspective, and gender differences accounting for higher limitations in women than in men [8
]. Obesity produces important effects also in psychological symptoms—such as negative self-evaluation, decreasing self-image, anxiety, and depression—which in turn determine reduced social activities [9
]. An important role for the development of psychological problems is played by the weight-based stigmatization associated with higher BMI that obese persons suffer from [10
] and is experienced as a negative stereotype, prejudice, and discrimination, reported in the areas of employment, education, health care, and media as well as interpersonal relationships [12
Taken together, these features related to impairments in physical and psychological functions and limitations in daily life constitute the profile of functioning and disability of obese subjects. Disability is defined by WHO with its International Classification of Functioning, Disability and Health (ICF) [13
], as the negative interaction, experienced by an individual with a health condition, between impairments at the body level and presence of barriers in the environment. Such a conceptualisation recognises that disability is not an intrinsic feature of an individual, but is also experienced and influenced by the environment in which the person lives. Obese patients' profile of functioning has been evaluated, using ICF-based methodologies, in two previous papers [14
]. The first reported the areas in which difficulties are reported, showing that areas connected to mobility and self-care are those most frequently reported as being limited. The second showed that impairments at the level of the body are much more closely related to limitations in performing activities than the effect of environmental factors.
Patient-derived outcome measures importance is increasingly recognised. Among these measures, health-related quality of life (HRQoL) is one of the most evaluated in patients with chronic conditions. In the field of obesity research, the evaluation of HRQoL was recognised by the United States Task Force on Developing Obesity Outcomes and Learning Standards [16
] (TOOLS), which recommended the use of SF-36 health-related quality of life and its short form (SF-12) as a generic HRQoL measure in obesity [17
]. Recent studies reported that increased body weight corresponds to a deterioration in the domain of physical functioning and general health score, particularly in women, while deterioration was less evident in mental functioning [18
]. Generic measures, however, do not address key domains relevant to obesity. Obesity-specific measures have been developed, including the impact of weight on quality of life (IWQoL), 74-item measure later reduced to the IWQoL-Lite of 31 items [20
], that better target obesity-specific issues [21
]. The utilisation of patient-derived outcome measure, in addition to clinical outcome such as weight loss, is relevant to understand or prevent the social disadvantages associated with obesity and its stigmatization. In a previous study, Sirtori and colleagues analyzed the relationship between HRQoL, disability, and obesity, underlying the importance of evaluating both HRQoL and disability in obese patients undertaking rehabilitative intervention, as the two outcome measures underline different and not transposable dimensions, thus reporting complementary information [22
The evaluation of outcomes in rehabilitation is strictly dependent on both the objectives of intervention as well as on the levels of disability and HRQoL that a patient displays. However, the effect of body weight on HRQoL and disability, measured according to ICF's biopsychosocial model, is not systematically evaluated. The relationship between increased BMI and functional limitations is of primary relevance, in particular in consideration with ageing trajectories. In fact, as reported by the results of a paper focussed on a large UK ageing study in which functional limitations were compared across subjects with different BMI groups, the excess of body weight in aged persons is associated with greater risk of impaired physical functions [23
]. What is lacking is an information on the degree of association between outcome measures—which enable to identify subjects with different degrees of disability and HRQoL reduction—and the severity of obesity, as well as sociodemographic variables such as sex and age. The identification of these relationships is of primary relevance to enable researchers and policy makers to face the challenge of the increasing burden of obesity-associated disability, health, and social costs.