Our study reveals that UHC participants have higher body fat distribution and are more prone to CVD risk factors (central obesity, blood sugar level, total cholesterol level) compared to the RHC and RL participants. Urbanization and economic development may bring improvement in the socio-economic status (SES), push a population to nutritional transition and adopt sedentary lifestyle [42, 43]. This makeover of lifestyle leads to the increased prevalence in central obesity, glycemic abnormality, dyslipidemia and hypertension irrespective of their place of residence [44, 45]. A number of previous studies show consistency with our study where urban women showed higher body fat distribution compared to their rural counterpart [46, 47]. For example, studies from India and western countries show positive association between education, income and body fat distribution [48, 49], but the trend is not universal [50–52].
Completed years of education of the spouses of the participants shows positive association with all the body fat measures in our study; this is in disagreement with [53, 54] or non-significant in some earlier studies [55, 56]. For example, a study conducted among Japanese women showed educational attainment of the spouses of the participants at high school level or lower had higher risk of obesity compared with women whose spouses attained higher level of education than the former group [54]. Our study contradicts to this finding; the literacy rate of the spouses of the participants showed positive association with central obesity. Perhaps, attainment of higher educational level of the spouses is associated with the higher social position and higher income leading to over nutrition and adoption of sedentary lifestyle. The prevalence of central obesity of rural and urban caste participants was 82.6% and 67.7% respectively which corroborates with some Indian studies [57, 58].
We found age at menopause as a significant predictor for higher blood sugar level. Early cessation of menstruation is associated with suppression of estrogen at a premature age. This phenomenon affects the insulin resistance by lowering the sex hormone binding globulin concentration of the blood and changing the body fat distribution from gynoid to android type [59, 60]. For example, in one US based study, women who experienced natural menopause before 40 years had a 50 percent higher chance of CVD related mortality than those reporting menopause at 50 years or later [61]. The UHC participants of our study reached menopause at an earlier age compared to the RHC and RL participants (48.74 ± 5.18). So, the early age at menopause might be a reason for the increased blood sugar level among the urban Hindu caste populations.
Our study shows that the RL participants are more prone to hypertension and have higher total cholesterol level compared to the UHC and RHC participants, but the trend is reverse for blood glucose level and in the prevalence of central obesity. We found an association between chewing of tobacco and increase in mean arterial pressure and decrease in body fat (PBF, subcutaneous fat related to whole body and trunk). A study conducted in an Indian city (Mumbai) shows all forms of tobacco use were associated with low body fat, irrespective of age, education, and religion (62). In our study, majority of the RL participants chew tobacco on a regular basis which might be a reason behind their low body fat and increased hypertension because tobacco produce free radicals that deplete antioxidants like Vitamins C, E, and carotenoids and cause oxidative damage to DNA, proteins and lipids [63, 64]. Studies show that consumption of anti-oxidant-rich foods such as green-leafy vegetables and fruits perhaps reduce the oxidative stress caused by tobacco; but the Lodha participants of our study lack these items in their dietary practices and thereby remains at a risk of tobacco induced oxidative stress.
Our study shows physical activity has an inverse association with the blood sugar level; this could be a reason behind the lower incidence of diabetes among the tribal participants. A recent study conducted among Chinese women reveals that a higher degree of physical activity was associated with lower blood glucose level regardless of sex, menopausal status and first-degree family history of diabetes [65]. Physical inactivity and obesity are critical and modifiable risk factors of diabetes; this could be a justification of the increased blood sugar level among the urban Hindu caste participants as most of them were found to be engaged in sedentary activities.
We observed an inverse association between consumption of meat and blood sugar level. Studies show that regular intake of meat leads to increased blood sugar level due to iron overload [66, 67], which is contradictory to our findings. Majority of the RL participants consume meat (poultry product) on a regular basis. Poultry product contains less calorie, highly digestible (with low levels of collagen) proteins, unsaturated lipids, B group vitamins and minerals like iron, zinc and copper and also has a low glycemic index value which helps in controlling the blood sugar level [68]. Future studies are required to confirm or refute this hypothesis.
Our study further revealed that working status of the participants is a significant predictor of body fat measures like waist-hip ratio and fat mass showing consistency with some previous studies [69, 70]. For example, in SWAN longitudinal cohort study it has been reported that physical activity has inverse association with changes in percent body fat, waist circumference, independent of aging and menopausal status [71]. The UHC participants of our study are mostly non-working, while the majority of the participants from RHC and RL are engaged in high intensity physical activity like agriculture and wood collection. This could be a reason behind the increased level of body fat among the urban participants compared to their rural counterpart.
Pregnancy and childbirth can additionally modify a woman’s risk of midlife obesity and CVD [72–74]. Women’s reproductive history may influence short and long term cardio-metabolic and cardiovascular trajectories later in life. Reproductive characteristics and pregnancy history in women are increasingly recognized in cardiovascular and obstetric society guidelines, with premature age of menopause and adverse pregnancy outcomes in particular now codified as risk-enhancing factors for CVD [75]. Our study showed that parity is positively associated with BMI, while age at first pregnancy shows inverse association with PBF and subcutaneous fat of trunk and positive association with the skeletal fat of arms and legs. Childbirth at a younger age and increased parity are independently associated with central obesity for women later in life due to increased stress or changes in the lifestyle factors which is in partial agreement with our study [72, 76]. For example, studies on Korean and US postmenopausal women showed similar results [73, 74]. Younger age at first childbirth is sometimes associated with disruption in education and occupational attainment which can increase the risk of obesity. Earlier exposure to high levels of estrogen by early pregnancy may lead to an increased body fat which in turn is speculated to influence CVD risk factors through complex interaction between oxidative stress, inflammation, the renin-angiotensin-aldosterone system, and the renal sympathetic nervous system [73, 74]. During pregnancy, the release of corticotrophin releasing hormone from placenta drive the hypothalamic pituitary-adrenal axis and cortisol concentrations in pregnant women may contribute to the pathophysiological mechanism of obesity later in life [78]. But, a recent study conducted among Korean postmenopausal women showed no significant association between age at first childbirth and central obesity after controlling for confounding variables [77]. We found an association between higher incidence of central obesity and higher parity among rural caste participants. Carrying a child to full term is associated with maternal metabolic changes and weight gain that persist after pregnancy. This could partially explain why RC participants have higher incidence of central obesity, unlike their urban counterpart. The RL participants of our study mostly conceived for the first time at a younger age (below 19) and show higher parity compared to the other two groups. But the prevalence of central obesity is not predominant among the Lodhas perhaps due to their high intensity physical activity.
We observed age of the participants to be a significant predictor for increase in body fat and mean arterial pressure showing consistency with some previous studies where degenerative effect of age has been reported [79, 80]. This could be attributed to the age specific changes at the cellular level, including oxidative stress, inflammation, and apoptosis, changing in the calcium plumping capacity, and overall myocardial deterioration and degeneration [81].
This exploratory study conforms to our hypothesis that there exists significant differences in body fat pattern and CVD risk factors between caste and tribal groups owing to the socioeconomic disparities, differences in reproductive characteristic and lifestyle factors.
There are certain limitations in this study. Estimation of fasting blood sugar level and the total lipid profile analysis, taking a larger sample size and a closer observation on the lifestyle practices (may be on a subsample) on the participants could have improved the findings of the study. Postmenopausal women become susceptible to health problems by reason of genetics, differences in attitude and perception and finally, their access to adequate health care services. Thus, inclusion of the data on these domains would give a better understanding of the cross-cultural difference in CVD risk factors of the caste and tribal group of the present study.