INTRODUCTION

Osteoporosis is a skeletal disorder characterized by compromised bone strength, predisposing to an increased risk of bone fracture.¹ Bone strength is highly correlated with its mass and mineral content.² Factors that are associated with bone density and quality are race, gender, age, reproductive history, body build, genetic, and dietary factors. According to Melton and Riggs,³ there are three fracture sites that are particularly characteristic of osteoporosis, namely the vertebrae, femoral neck, and radius, and they constitute an enormous public health problem in developed countries.

That very little attention is being paid to the problem of osteoporosis among black South African women is partly due to the notion among healthcare practitioners that black South African women are less likely to suffer from osteoporosis than their Caucasian counterparts. It may also be due to the behavior of African women who may treat the physiological and clinical manifestations of the transition to menopause as being natural and due to old age.

One-third of all women over the age of 65 years have one or more vertebral fracture, which may be associated with severe and sometimes prolonged pain, spinal deformity, and loss of height.² Hip fracture, which affects one in three who survive to extreme old age, has a mortality rate of 12 to 20% at 6 months and results in increased deficiency and/or hospitalization in the majority of survivors.³

In developing countries, including South Africa, osteoporosis among black South African women has failed to attract adequate attention. A number of reasons can be cited for this poor knowledge and, hence, neglect of this condition in a select population group in South Africa. First, healthcare policies are geared toward giving priority to infectious diseases (high on the list is human immunodeficiency virus), as well as noncommunicable diseases such as hypertension, diabetes, and coronary heart disease. Second, limited resources for timely diagnosis and the paucity of information and data on osteoporosis among black South African women have contributed to this neglect.⁴ The present gap in the knowledge and the enormity of the problem of osteoporosis among black South African women need to be addressed. Early detection of the BMD being compromised as women transit from premenopause through perimenopause could provide a guide for averting the consequences of osteoporosis after menopause. Information derived from this study highlights the need for this type of surveillance in other developing countries with similar notion of the needs of women as they transit to menopause and beyond.

MATERIALS AND METHODS

The participants in this study were recruited from the group of women who had participated in another study looking at the sociodemographic and psychosomatic characteristics of menopausal black South African women. All participants were, at the time of this study, resident in Ga-Rankuwa, Soshanguve, and Odi districts of northern Pretoria, South Africa. The areas covered by these districts are semiurban and the population consists of people who have migrated from the North West of South Africa and Limpopo Provinces, seeking better opportunities in the Gauteng province.

The study consisted of 68 women aged between 32 and 77 years, who were classified into three distinct groups based on their menstrual history:

Following ethical approval for the study by the Institutional Review Committee of Sefako Makgatho Health Sciences University, each of the women signed an informed consent form to participate in the study. Participation in the study necessitated each participating woman providing the following accurate information of relevance:

MEASUREMENTS

The BMD at the femoral neck and the lumbar spine (L1-L4) expressed as gm/cm² was measured using DEXA with Hologic 4500 densitometer (Hologic Inc.; Massachusetts, USA). The radiation dose with this method is negligible at 0.28 μGy. Body weight was measured as a standing weight (without shoes) using a calibrated electronic scale. Body mass index (BMI) was calculated as ratio of weight over height (in meters squared). The DEXA result of BMD was expressed as T-score based on WHO classifications.⁵ The statistical tool used to analyze the results was Statistical Package for the Social Sciences, version 22.0.

The WHO definitions of osteopenia and osteoporosis (Table 1) used to interpret spine and hip BMD results from DEXA in white women are as follows (there are no estimates of DEXA BMD values for black South African women):

RESULTS

All the women who participated in the study were found to be healthy with none of the above-listed medical conditions. In Table 2, the average age [± standard deviation (SD)] of the women in this group was 37 years (±2.98). Based on the DEXA results in this cohort, 2 of the 8 premenopausal women (25%) were found with evidence of osteopenia. The two women who were diagnosed with osteopenia had DEXA results as (—1.30) and (—1.16).

Table 3 illustrates the average age (±SD) of the women who were in their perimenopausal state and this was 45.7 years (±4.0). Based on the DEXA results for this group, 2 of the 28 perimenopausal women (7.1%) were adjudged to have evidence of osteopenia with DEXA results of (—1.42) and (—1.79).

Among the women who were defined as having attained menopause (Table 4), the average age (±SD) of the women was 53.2 years (± 5.1). From this group, 11 of the 32 women (34.4%) were found with evidence of osteopenia and an additional 8 women (25%) had evidence of osteoporosis. The average age of women who had osteopenia was 55.6 years as compared with an average age of 68.0 years for those who were diagnosed with osteoporosis. The DEXA results for this group ranged between —1.20 and —2.18 for those who had osteopenia and between —2.65 and —3.21 for those with osteoporosis.

Table 5 reflects the composite evidence of osteopenia or osteoporosis among the three classified groups of women. Out of the 68 women, there were 22.0% cases of osteopenia cut across all three stages of menopause and an additional 25% of the cases of osteoporosis only in the postmenopausal group.

DISCUSSION

The study shows that there was 22% incidence rate of osteopenia in the whole study group, while 11.76% of the participants were osteoporotic (uncorrected for age). Osteopenia was detected even among premenopausal women—an indication that the process leading to bone mineral resorption could have started long before the women became menopausal. This finding is partly supported by the work of Finkelstein et al,⁶ which emphasizes that bone loss is accelerated from late perimenopause to menopause.

Obesity was recorded in all three groups of women Table 6 and more especially among the premenopausal women. This is contrary to the theory that obesity promotes increased bone mass as a result of peripheral conversion of androstenedione to estrone. Furthermore, previous reports^6-9 did indicate that African black women possess greater muscle mass and would, therefore, be expected to experience less of the characteristics of the consequences of menopause. According to two independent studies, one conducted in South Africa and the other in the United States, which appeared jointly in one publication,¹⁰ the cortical bone histomorphometry11 of the iliac crest in normal black African adults and Afro-Americans is thicker than their white South African counterparts and the Caucasians in the United States. The study by Solomon,¹² although was conducted many years ago, also elaborated on the fact that black South African women have stronger bone structure than their white counterparts. This may have contributed to less focus being placed on the problems of bone mineral loss during the menopause years among black South African women.

In the current study, there were 16 women who were obese among the postmenopausal women (50%). This may be attributable to a change of lifestyle of African women who lead a more sedentary lifestyle after menopause, with a diet rich in animal protein as a result of urbanization and an increase in a negative calcium imbalance. There is an increase in phosphate, which then leads to an increase in parathyroid hormone—an increase of which promotes urinary calcium excretion.

Large numbers of black population migrate from rural areas to cities to seek better work opportunities. This movement is accompanied by the change in lifestyle and dietary habits, which lead to major health consequences. The article by Seftel¹³ has clearly highlighted the effect of urbanization and Westernization in the black South African women with development of noncommunicable diseases such as hypertensive disorders, atheroma with myocardial infarction, as well as diabetes type II. The two studies by Kruger et al^14-16 also support the hypothesis of Seftel that migration has a deleterious effect on the population because of the dietary and lifestyle changes, which may contribute to low bone mass.

A study done in Thailand comparing the effect of urbanization on two groups, namely, the urban and rural populations, clearly indicated that BMD in the rural population was higher in comparison with the urban population. This study has raised concerns that traditional ideas of nutrition are gradually being eroded and replaced by the Western world lifestyle, which is likely to lead to an increase in the prevalence of osteoporosis. This finding has been reinforced by the work of Yang et al¹⁷ and that of Ponjgchaiyakul et al,¹⁸ both of whom have also reported that rural population has a lower incidence of osteoporosis than their counterparts in the urban settings.

The study conducted in Morocco¹⁸ has added the information about the effect of parity and dietary habits of women, with calcium deficiency and an overall consequence of bone demineralization. These factors seem to interact with one another in the reduction of BMD. Vitamin D deficiency and veiled clothing with less exposure to sunlight were cited as factors in this study, and the same findings had been corroborated by a similar study conducted in Saudi Arabia.¹⁹

The BMD was found to be higher among postmenopausal women of Trinidad and Tobago. This finding is attributed to strong genetic makeup, healthy lifestyle, and probably due to low European admixture as well as the use of thiazide diuretic.²⁰

The overemphasis of the protection from osteoporosis among African-American women is mainly due to disparity of osteoporosis screening between them and their white counterparts. The fact that African-Americans have higher BMDs than Caucasians throughout life does not mean that postmenopausal bone loss that occurs in Caucasians will not manifest among the African-Americans.^21-23 The present study also attests to the fact that black African women are not immune to the effects of bone mineral loss during the menopause years.

Large studies aimed at identifying the prevalence of osteoporosis have failed to include a large population of Afro-American women. However, three articles have indicated that osteoporosis is a reality among African-Americans with an incidence rate ranging from 15 to 28%. Although the articles reported on studies conducted with small sample sizes, however, their common finding points to the existence of the reality of osteoporosis existing among women of African descents living in the United States.^24-27

A study by Solomon²⁸ in South Africa, which was conducted more than 30 years ago, did not find any osteoporosis among black South African women. This study assessed BMD by using anteroposterior radiographs of the second metacarpal bone. This method cannot be extrapolated to the hip as well as to the vertebrae in determining the BMD. In contrast, more recent studies by Kruger et al²⁹ and the work of Conradie et al³⁰ have confirmed that there is osteoporosis among black South African women. The current study, although from a small sample population of black South African women, further provides additional evidence that corroborates previous reports of the studies alluded to in the present study.

CONCLUSION

Osteoporosis exists among black South African women. The inclusion of urbanization among the risk factors for this population is necessary and relevant to the fact that the occurrence of osteopenia and osteoporosis is not confined to Caucasians. The need for an osteoporosis clinic, with a multidisciplinary approach and reinforcement of screening strategies, is a recommendation, especially in academic hospitals in South Africa where adequate logistics are likely to be available.