INFLUENCE OF AGE, SEX AND NUTRIENT INTAKE ON BONE DENSITY OF RURAL NIGERIAN ADULTS

Abstract

The influence of age sex, and nutrient intake on bone density was determined in 97 rural adult Nigerians (65 males and 32 females). Bone density indices were calculated from measurements on radiographs of the second metacarpal bone. Habitual dietary intake was ascertained through food frequency questionnaire. Identical food samples (as eaten) were chemically analysed for estimation of mean daily intake of energy, protein, calcium and phosphorus . A minimum of eight-hours fasting urine and blood samples were analysed for biochemical markers of bone metabolism. This included urinary calcium, hydroxy proline and creatinine, serum total calcium, phosphorus, magnesium, albumin, total proteins and alkaline phosphatase. The diet was essentially vegetarian with about 80% of the protein and calcium derived from plant sources. The daily intake of energy, protein and phosphorus were significantly higher in the males (p < 0.05). Bone masa (cortical area) but not bone quality (percentage cortical area) was significantly higher in the males (p<0.05) compared to females. Bone Loss was observed in both sexes after 40 years of age, but the influence of age on bone density was greater in the females. The rate of bone loss was approximately 5% and 2% per decade in females and males respectively. Bone density correlated positively with age in the younger females ( r = 0.60; p<0.05) and negatively in the older women above 50 years ( r = -0.759; p<0.05). The relationship between bone and age was influenced by dietary calcium in the younger females. An association was observed between mean dietary calcium and bone mass in males (r = 0.34, p<0.05) and bone quality in the younger females (r = 0.639; p<0.05). The relationship was influenced by energy intake In the males but not in the younger females. No association was observed between dietary calcium and bone density in the older females. The serum parameters showed no sex variation, with the exception of corrected serum calcium which was higher in the males (p<0.05). Serum albumin correlated with serum calcium in male and female subjects (r = 0.65; p<0.05) and (r = 0.75,p<0.5) respectively, and also with bone quality in males (r=0.32; p<0.05) and older females (r= 0.83; p<0.05). Urinary hydroxyproline correlated with urinary calcium in both sexes (r = 0.813, P<0.05 ) and (r = 0.844, p<0.05) respectively. In general subjects showing higher calcium excretion (Uca/Crt > 0.05) tended to have lower bone density indices. Bone density was related to calcium excretion (r = -0,794, P<0.05) as well as to hydroxyproline excretion (r = -0.739, p<0.05) in the older females. The negative association between urinary calcium and bone mass ( r = -0.39, P<0.05), in the males, suggests an indirect relationship between bone accumulation and calcium retention.

The findings from this study show that adequate nutrient intake is important especially during the developmental stage with profound effect on ages-onset bone loss.