The present study based on data from the 2013 NHS showed that 45 % of the Brazilian adult population reported having at least one NCD, and that the most frequent chronic diseases were hypertension, spinal/back pain, diabetes, arthritis/rheumatism, depression, and bronchitis/asthma. The presence of at least one NCD was more frequent among women, individuals 55 years and older, individuals with low schooling levels (illiterate and incomplete elementary school) and people living in the southeastern, southern and central-western regions of Brazil. Five of the diseases surveyed were more prevalent in the stratum of lower schooling. Physical limitations caused by NCDs were reported more frequently among those with lower schooling and those without any private health insurance. These results indicate the presence of social inequalities in the distribution of NCDs in the Brazilian population, and greater physical limitation due to these diseases among more vulnerable populations.
Morbidity data are important for managing healthcare systems and for planning and evaluating healthcare service provision. Analysis of such data with a focus on inequalities may indicate ways to address existing disparities [2, 3]. However, such information is often unavailable in many middle- and lower-income countries .
The literature from high-income countries suggests higher prevalence of NCDs in less educated populations, a finding that is consistent with the results found here for Brazil [4, 11].
A survey conducted in eight countries (Denmark, France, Germany, Italy, Japan, Netherlands, Norway and the United States), investigating NCD morbidity (including hypertension, diabetes, ischemic heart disease, allergies, arthritis, congestive heart failure and chronic pulmonary disease), found that 55.1 % of the adults aged 18 and over reported at least one chronic condition . The prevalence of having at least one NCD observed in the present study (45 %) was higher than that observed in previous studies based on the 2003 National Household Sampling Survey (PNAD)  (40 %) and the 2008 PNAD  (40.6 %). This higher level is likely the result not only of continued aging of the population but also from expansion of access to diagnoses of these diseases in Brazil over the past decade.
The greater prevalence of the majority of the self-reported NCD found among women was concordant with the literature [13, 15, 16]. This situation has been attributed to the fact that women seek out and use healthcare services more than men do, thus resulting in greater opportunity for being diagnosed. Studies have attributed this to women’s greater perception of the physical signs and symptoms of these diseases, which is facilitated by attending healthcare clinics more frequently [7, 16, 17]. The difference in prevalence between the sexes was 20 % in 2008 (adjusted PR = 1.20)  and increased slightly to 24 % in 2013 (adjusted PR = 1.24). These differences may be explained by higher life expectancy among women, resulting in an increased disease burden, as well as an increased demand for health services and thus a greater opportunity for diagnosis among women [14, 16, 17].
The greater occurrence of NCD with increasing age is coherent with the literature and results from the aging of the population and the greater disease burden among elderly people [1, 6, 7].
Analyses in Brazil from the PNAD 2008 revealed that, after adjustment for age, sex and other variables, there was higher prevalence of reporting at least one NCD among people living in urban rather than rural areas, and among those living in the southern region of the country . This finding was attributed to greater access to healthcare services in these areas. Comparison with previous PNAD surveys shows that there has been a progressive increase in the prevalence of NCD among the rural population: from 37.7 % in 2003  to 39.6 % in 2008  and 43.4 % in 2013. This trend is indicative expansion of access to medical diagnoses for people living in rural areas.
Findings from this study also indicate higher NCD prevalence among people with low versus higher levels of education. This pattern was detected in several studies conducted in developed countries [18–20]. Also in Brazil, previous studies have shown similar results including those from the World Health Survey 2003  and PNAD 2003 . In 2008, NCDs were more prevalent among individuals with lower education levels, except for tendonitis/tenosynovitis and cancer, which occurred predominantly among people with higher education levels [7, 14].
In India, a recent survey showed the opposite; groups with higher income had higher self-reported NCD prevalence as compared with low-income groups, probably due to under-diagnosis and underreporting of disease among the poor , since populations with higher socioeconomic status in low and middle income countries usually have better access to health care [23, 24]. There may be organizational, social, cultural and/or financial barriers that limit access to health services among populations of low socioeconomic status, all of which could affect the opportunity to diagnose NCDs [18, 19, 25, 26].
Epidemiological studies on self-reported non-communicable diseases may therefore underestimate the NCD prevalence in groups of low socioeconomic levels. It is therefore recommended that correction measures be used . Unlike the findings from India and some other middle income countries [22, 25], the NHS 2013 showed greater prevalence of self-reported NCDs in the population of low schooling levels in Brazil. Thus, Brazil’s situation is more similar to what is seen in populations in high income countries like the United States, Canada and European countries [18–20]. This result is likely explained by greater access to healthcare services in Brazil for poorer populations, due to the National Health System (SUS), which is public, universal and free-of-charge. The SUS includes broad segments of the population and has been associated with reductions in socioeconomic inequalities in health and healthcare [27, 28].
NHS 2013 revealed higher prevalence of hypertension, diabetes, spinal problems, arthritis, chronic renal failure and stroke among those with lower schooling levels. These associations had also been observed in PNAD 2008 , with the exception of stroke, which was not investigated. On the other hand, higher prevalence of cancer and musculoskeletal disorders were observed in the strata with greater schooling, as had been observed in 2008 .
In addition, higher prevalence of smoking, obesity, poor nutrition and low levels of physical activity in the population with less education explains the higher prevalence of hypertension, diabetes and chronic renal failure among these populations [2, 6, 29, 30].
It is recognized that pains and musculoskeletal problems affect a large portion of the population resulting in economic impact and loss of quality of life. Brazilian studies  showed that diseases of the spine/back affect a large portion of the population with less schooling. A review study indicated that educational level has an impact on the duration and recurrence of episodes of back pain. Individuals with more education have more favorable evolution of back pain .
Only two diseases presented greater prevalence in those with higher schooling: cancer and musculoskeletal disorders. In relation to cancer, a study conducted in European countries  showed a profile similar to that found in the present study, with lower cancer prevalence among individuals with low schooling levels. In Brazil, studies have shown that musculoskeletal disorders and tendonitis are more frequent among people of higher socioeconomic levels [7, 33, 34], which may be connected with their greater presence in the labor market, greater risk of developing the disease, greater awareness of the risks of repetitive exertion, and greater access to diagnoses and longer life expectancy.
NHS 2013 revealed that for all the diseases investigated with the exception of chronic renal failure, significantly greater prevalence of severe or very severe limitations were observed among individuals with lower schooling levels.
In relation to musculoskeletal diseases, the literature suggests that their greater impact in more socially vulnerable populations contributes towards worsening these individuals’ disabilities and exacerbating difficulties finding and remaining in work . It has been recognized that a high percentage of the population demands healthcare services because of these problems and that the frequency of limitations on daily activities is high, including time off work, retirement due to disability and days spent bedridden .
Even in relation to cancer and musculoskeletal disorders, which are more prevalent in the strata with greater schooling, the impact in terms of severe and very severe limitations is greater in the segment with lower schooling. Social inequalities relating to such limitations have many causes: lower and later access to services, attendance of lower quality, fewer resources, poor living conditions, lack of information for enabling good treatment, lack of follow-up and poor disease management. It has been suggested that appropriate restructuring of attendance and care for patients could reduce inequalities relating to limitations of daily activities . Studies evaluating inequalities in the limitations caused by NCDs remain scarce, especially in less developed countries .
The choice to adjust rates by age, sex and region was important and justified by the rapid demographic transition in the country, with different gains in life expectancy by sex. Women live longer, due to deaths by external causes among men, making it important for the adjustment of NCD prevalence by sex. There are also significant regional differences in the age composition. Adjustment by Region also becomes relevant considering regional differences in access to health services as well as differences in the educational attainment.
There was higher prevalence of some NCDs (cancer and tendonitis) in the population without private health insurance . Previous studies have identified that people with health insurance have more access to health care, lower prevalence of risk factors for NCDs and greater access to preventive cancer screening [37–39].
In recent years, the portion of Brazilians in the formal labor market increased and this increased access to employer-paid private health insurance [37, 38]. The expansion of coverage of public and private health services could explain the reduction of differences in NCD prevalence among individuals with and without private health insurance. However, when considering the degree of limitation, individuals with NCDs who do not have health insurance presented a higher prevalence of intense physical limitation for several NCD (hypertension, asthma, spinal column problems, depression, cancer, chronic renal failure) than those who have insurance. This finding may be the result of delayed access to health services or lack of resources for the treatment and management of these diseases by people without private health insurance [37–39].
This study has advantages and limitations. The main advantage is the large nationally representative sample of the population. Another advantage of the study is its internal validity, given that the NHS produced good quality data [11, 12].
On the other hand, the study has limitations inherent to its cross-sectional nature. The results are based on self-reported data and thus subject to recall bias. In addition, disparities in disease prevalence are associated with differential access to health services among groups of different socioeconomic levels . Thus, a higher prevalence may be related to opportunities for diagnoses made by health professionals, which could partially explain some of the regional and socioeconomic differences observed here [36, 40].
Moreover, our analysis did not include an important indicator of SES, income, since this information was not available when our analysis was implemented. Thus, the magnitude of differences according to schooling level observed in the present study may have been underestimated, given that the segments with lower schooling level tend to have less access to healthcare services and to diagnostic tests and hence underreport the presence of morbidities.
There may also have been differences in the prevalence found in relation to those of other studies because of differences in the number and type of health problems and chronic diseases that were included in the survey; the age group investigated; the sampling method; the questions and words used in the questionnaire; the access to healthcare services among the population surveyed; and the type of respondent (the person concerned or another member of the family speaking on his behalf), among others.
In 2011, Brazil launched a Strategic Action Plan for NCDs, establishing actions and targets to reduce premature mortality (deaths between the ages of 30 and 69) by 2 % per year, and reduce the prevalence of associated risk factors [8, 9]. Premature mortality from NCDs has been declining in Brazil [6, 9, 29]. Several public policies encouraging healthy diet, reducing salt in food, creating public spaces to support physical activity, and mandating smoke free environments, in addition to investments in primary care and diagnostic and specialty services have been implemented [6, 8, 9].