Prevalence of Non-Communicable Diseases and Associated Factors in South Africa: Evidence from National Income Dynamics Survey, 2008-2017

Obasanjo Afolabi Bolarinwa (  bolarinwaobasanjo@gmail.com ) University of KwaZulu-Natal https://orcid.org/0000-0002-9208-6408 Olalekan Seun Olagunju Obafemi Awolowo University Eugene Budu University of Cape Coast Abdul-Aziz Seidu James Cook University College of Public Health Medical and Veterinary Sciences Ismail A Odetokun University of Ilorin Faculty of Veterinary Medicine Ahmad I Al-Mustapha University of Ibadan Faculty of Veterinary Medicine Simangele Azande Shezi University of Kwazulu-Natal Bright Opoku Ahinkorah University of Technology Sydney


Introduction
The increasing incidence of non-communicable diseases (NCDs) such as cardiovascular diseases, cancers, diabetes, and chronic respiratory diseases presents a global health crisis [1]. In 2016, the global NCD-related deaths of 41 million were 14% higher than the 36 million deaths reported in 2008 [2,3]. Approximately 81% of these deaths occurred in low-and middle-income countries (LMICs) [2]. It has been anticipated that NCDs may account for 46% of sub-risk leading to a high prevalence of NCDs [22]. Hence, this study aimed to determine the prevalence and examine the risk factors associated with NCDs' occurrence among the South African adult population from 2008 to 2017.

Data And Methods
Description of the study area The study was conducted in SA, located in the Southernmost part of Africa with a population of 53.5 million people and constitutes about 8.3% of Africa's population size [23]. In addition to having one of the highest prevalence of HIV/AIDS globally, SA continues to face high NCDs rates, with 41% of all deaths being caused by NCDs [24].
The rationale for the study Based on previous studies, among the male population, 43% had raised blood pressure, 46% were physically inactive [25], while 31% had raised blood cholesterol [26]. On the other hand, among the female population, 41% had raised blood level, 56% were physically inactive, and 37% had raised blood cholesterol.
In light of this, the government of SA initiated the strategic plan for the prevention of NCDs in 2013 by putting in place a regulatory framework around salt consumption in addition to the intervention to limit access to tobacco with the view to achieving a signi cant reduction in the prevalence of NCDs and associated mortality [27].

Target population
The population considered in this study were adults (males and females) between the ages of 18 and above in SA. Respondents who were less than 18 years were excluded from the study.

Data source
This study extracted the data of both male and female older adults (i.e., at least 18 years and above) in South Africa from the overall data collected from a sample of adults in the National Income Dynamics Study (NIDS). The NIDS is the rst nationally representative household-based longitudinal (panel) survey in SA -implemented by the Southern Africa Labour and Development Research Unit (SALDRU) at the University of Cape Town every two years-based on which accurate and reliable estimates of socio-economic (poverty, wellbeing, inequality, education, human capital formation, labour market participation and economic activity, vulnerability and social capital) demographic (fertility, mortality and household composition and migration) and health parameters were derived and routinely monitored [28].
In the rst year of the surveys in 2008, a nationally representative sample of 28,000 individuals in 7,300 households was interviewed and followed up to the year 2017. Also, any new members of the sampled household were interviewed but not followed-up. Thus, a total of ve surveys have been conducted so far.
Being a feature of a panel study, there were attrition cases among the Whites, Indian/Asians, and high-income respondents. So, to reduce the effect of sampling bias and coverage error age in the fth wave (2017) as a result of attrition, an extra (top-up) sample of 2,775 individuals was added. Hence, all the previously released weights (design, calibrated and panel waves) in waves one to four were recalculated while the current weight in wave (2017) considered the attrition rate and top-up sample inclusion. After considering the study population, the total sample size for this study was 64,735 with each year sample size as follows 2008 was 11,051, 2011 was 13,793, 2012 was 13,753, 2015 was 12,427, and 2017 was 13,712. More information about the study can be obtained from the NIDS website: http://www.nids.uct.ac.za/.
The 2008-2017 datasets were formally requested and obtained from the Department of Planning, Monitoring and Evaluation (DPME) and SALDRU. The datasets have been blinded and therefore pose no threat to any interviewed respondent, households, community or nation.

Outcome variables
The study's main outcome variables were high blood pressure, diabetes, asthma, heart problem, cancer, and at least one NCD. Blood pressure, diabetes, asthma, heart problem, and cancer were derived from questions that asked respondents whether they had been diagnosed with any of these diseases. For each of them, the responses were 'yes' or 'no'. Those who answered 'yes' to any of the questions were considered having blood pressure, diabetes, asthma, heart problems, or cancer. Out of these ve NCDs, a composite variable 'at least one NCD' was generated and represented respondents who had been diagnosed with either blood pressure, diabetes, asthma, heart problem or cancer.

Explanatory variables
Ten explanatory variables were considered in this study. The variables were age (18-24, 25-34, 35-44, 45-54, 55-64 and 65+), gender (male and female), employment status (unemployed and employed), marital status (never married, married, living with partner, widow/widower and divorced/separated) and population group (African, colored, Asian/Indian and White). Other explanatory variables were religion (no religion, Christianity, Islam, Traditional religion and others) and education (no formal education, primary, secondary and tertiary). Level of satisfaction with life (dissatis ed, satis ed and very satis ed), alcohol consumption (never, rarely, once a week and every day) and frequency of exercise (never, rarely and once a week) were also considered as explanatory variables. These variables were not selected a priori but based on their availability in the datasets and previous studies [29,30], nding signi cant factors associated with non-communicable diseases.

Statistical analysis
Data used in this study were processed and analysed using STATA version 16.0. Both descriptive and inferential statistics were employed. The analysis began using descriptive statistics of frequency and percentages to present the respondents' demographic characteristics for the ve survey waves (2008, 2011, 2012, 2015 and 2017). This was followed by the use of bar charts and line graphs to show a graphical representation of the proportions of respondents diagnosed with blood pressure, diabetes, asthma, heart problem, cancer and at least one of these diseases, respectively. Next, the ve datasets were appended, and Pearson's chi-square test of independence was used to examine the association between the explanatory variables and the outcome variables. Finally, both bivariate and multivariable binary logistic regression was used to assess the risk factors for blood pressure, diabetes, asthma, heart problem, cancer and at least one of these diseases. Results were presented as crude odds ratios (cORs) and adjusted odds ratios (aORs), with their corresponding 95% con dence intervals (CIs) signifying their level of precision. Statistical signi cance was declared at p<0.05. Sample weight was applied to cater to under and oversampling across the outcome and explanatory variables [26,31,32].  Over the 10 years, the highest prevalence of high blood pressure (17.3%), diabetes (5%), asthma (4.1%), heart problem (2.7%) was recorded in 2012. However, the highest prevalence of cancer was recorded in 2015 (1.3%) ( Figure 1). In terms of at least one non-communicable disease, the prevalence reduced from 23.0% to 17.4% between 2008 to 2011, increased to 23.8% in 2012, reduced further from 23.8% to 15.2% in 2015 and increased to 18.9% in 2017 ( Figure 2).  Table 2. The chi-square test results indicated statistically signi cant associations between the socio-demographic characteristics and the occurrence of blood pressure, diabetes, and at least one NCD. Conversely, exercise and satisfaction level of life showed no statistical signi cance with asthma. Similarly, exercise had no statistically signi cant association with heart problems.

Discussion
This study, to the best of our knowledge, provides the rst report of the prevalence and factors associated with the occurrence of major NCDs among the adult South African population. We found out that the occurrence of high blood pressure among the adult population in South Africa is of major concern as compared with diabetes, asthma, heart problems and cancers with age, gender, marital status, religion, level of satisfaction, education, and exercise all playing major roles in the reporting of these NCDs. It's also important to know that high blood pressure is regarded as the world's most prevalent NCD affecting billions of persons, including Africans [33,34].
This study identi ed respondents age to be associated with blood pressure, heart problem, diabetes, cancer and asthma. This was observed more in adults aged 65 + than in other age groups. Similarly, some previous reports across the world have indicated a positive relationship between age and most NCDs, especially high blood pressure [34][35][36][37][38]. In old adults, due to ageing, major blood vessels in the body come constricted, leading to high blood pressure (39), possibly resulting from the cumulative effects of the adults' poor behavioural habits [39]. These suggest that more priority should be paid to the treatment of NCDs in adults.
The in uence of gender in the occurrence of high blood pressure, asthma, heart problem, diabetes, and cancer was highlighted in this study, similarly, as observed by Esmailnasab et al. [37]. Females of the 10 years were more likely to carry these NCDs. This is in contrast to studies by Gao et al. [36] and Arab et al. [40] who reported high blood pressure and other NCDs had been reported to occur more in men than women. This observation could be attributed to biological sex difference [41], an insu cient number of females or the disproportionate number of gender type recruited in this study. This needs to be explored further to determine why more women in SA are at higher odds of having NCDs. In contrast to the ndings of Adhikari et al., [42] women in SA tend to get engaged in behaviours that increase the occurrence of NCDs.
Widowed respondents, were more likely to have high blood pressure, asthma, heart problem, and diabetes when compared to those who were married. This result is unexpected as these widows could have been exposed to psychological, psychosocial, emotional, and physical trauma or stress. These are associated with several cardiovascular symptoms in humans, including cardiac death [43][44][45].
We found that even though most respondents were associated with a religion, is unprotective from having high blood pressure, asthma, diabetes, and heart problem compared to those who had no religion. This is contrary to the ndings of Meng et al. [46], who suggested that religion bene ts control and prevention of blood pressure in patients. The scenario is similar to other cardiovascular diseases and NCDs [45]. Religion and spiritual coping decreased the risk of hypertension among African American women, even when they are exposed to stress [47].
This study showed that smokers were at higher odds of having blood pressure, asthma, heart problem, diabetes, and cancer than non-smokers. This observation is consistent with previous ndings [41,45]. Lack of behavioural risk factors such as smoking could serve as a protective effect against most NCDs [41].
Exercise is judged to be very protective as a sedentary lifestyle is regarded as a risk factor for many cardiovascular diseases [48]. Regular exercise is regarded as an important activity for preventing high blood pressure [49,50] and for improving life expectancy [51]. Improvement in the quality of life of patients with heart disease who participated in regular exercise has also been con rmed in a study [48]. In this study, respondents who exercised once a week were less likely to have high blood pressure, cancer and at least one NCD compared to those who never exercised. However, other studies found an inverse relationship between exercise and the risk of high blood pressure [41,52]. Regular exercise bene ts the health, lower high blood pressure and reduces the risk of cardiovascular diseases. Thus, increasing physical activity levels should be a major goal at all levels of health care [53].
Our study noted that lower odds of high blood pressure, asthma, heart problem, diabetes were found among respondents with tertiary education, compared to those with no formal education. This nding is corroborated with a study that concluded that education was signi cantly associated with the occurrence of NCDs [54,55]. Also, respondents who are very satis ed with life were more likely to have high blood pressure and cancer than those who were dissatis ed with life. Higher socio-economic status is regarded as a risk factor for some cardiovascular diseases, especially hypertension [35,36,56,57]. It is believed that those who are satis ed with life have more purchasing power for feast conveniently with little participation in exercise and this lifestyle easily predisposes them to NCDs [41].

Strength And Limitations
The study's major strengths were the large study participants, representativeness of the country and these surveys were conducted by well-trained indigenous enumerators who were able to capture the dataset accurately and timely. Additionally, the study gave speci c and overall insights on NCDs prevalence and associated factors in SA for the 10 years. These results could be used in developing major behavioural interventions toward reducing NCDs prevalence with special consideration of the associated factors. The study's limitations were that this study did not incorporate the qualitative data. Also, the study's crosssectional nature makes it di cult to ascertain the true cause and effect relationship between NCDs and associated factors.

Conclusions And Policy Implications
This study utilized prevailing associated factors based on the literature gap about non-communicable diseases prevalence in South Africa for the period of 10- year. The study concluded that among the NCDs, high blood pressure and diabetes were the prevailing diseases with the highest prevalence across the 10-year while cancer has the lowest prevalence. Socio-demographic factors associated with a high prevalence of NCDs were respondents older than 65, those who were females, widowed and those without education or primary education whilst the behavioural factors were respondents who were smokers, those who engage in less physical activities or exercises and those who reported having been satis ed with life. South Africa's department of health and other health agencies need to strengthen existing policies and develop new interventional frameworks that will deliberately put into consideration various factors contributing to the high prevalence of NCDs identi ed in this study. This will not only reduce the NCDs prevalence in the country but will also reduce the morbidity and mortality levels. Trends of at least one non-communicable disease from 2008-2017