Influência da suplementação de cálcio sobre os níveis de chumbo e indicadores da exposição ao chumbo em mulheres na pós-menopausa

Abstract

The accelerated bone loss that occurs during menopause and becomes more prone in the postmenopausal period is mediated by the ending of estrogen production. This bone loss can be a threat for women in this period of life concerning to the lead toxicity. Around 95% of the lead accumulated in the body is stored in the bones and may be mobilized to the bloodstream during bone demineralization, posing a potential risk. On the other hand, an adequate calcium supplementation seems to reduce gastrointestinal lead absorption. However, studies carried out in the United States revealed relatively high lead levels in calcium supplements. In the present study, we evaluated the content of lead in calcium supplements available in Brazil. We also investigated the effect of calcium supplementation and bone diseases on blood lead levels, δ-aminolevulinic acid dehydratase (δ-ALAD) activity, δ-ALAD reactivation index and antioxidant enzymes activities in postmenopausal women non-occupationally exposed to lead. Two studies were conducted, one with a cross-sectional design and another with a prospective design. Biochemical parameters were evaluated in both studies. In the prospective study these parameters were evaluated before and after three months of calcium supplementation. A total of 11 calcium-based products were selected and their lead and calcium content were determined by graphite furnace and flame atomic absorption spectrometry, respectively. Blood lead was assessed by inductively coupled plasma mass spectrometry and bone mineral density (BMD) was evaluated at the lumbar spine (BMD L1-L4) and femoral neck (BMD femur) by dual energy X-ray absorptiometry. δ-ALAD activity and antioxidant enzymes activities were determined in whole blood using spectrophotometric methods. δ-ALAD reactivation index was determined by measuring enzyme activity in the presence of 3 mM ZnCl2 and 10 mM DL-dithiothreitol. The lowest lead content per gram of calcium was found in bonemeal (< limit of quantification) and the highest lead content per gram of calcium was found in dolomite (2.3±1.2 μg. g-1 of measured calcium). No differences were observed in δ-ALAD activity or δ-ALAD reactivation index between postmenopausal women with and without bone diseases, both in the cross-sectional and in the prospective study. In the prospective study, three months of calcium supplementation increased blood lead levels in osteopenia (4.6 μg/dL) when compared with control group (3.7 μg/dL) and decreased alkaline phosphatase activity in all groups: control (66.2 vs. 71.9 U/L before the beginning of the treatment) osteopenia (67.1 vs. 71.1 U/L) and osteoporosis (83.9 vs. 86.1 U/L). Catalase (CAT) and superoxide dismutase (SOD) activities were not different between postmenopausal women with and without bone diseases, both in the cross-sectional and in the prospective study. However, gluthatione peroxidase (GPx) activity was significantly higher in osteopenia group (23.32 μmol NADPH/g Hb/min) as compared to control group (18.56 μmol NADPH/g Hb/min) in the cross-sectional study. This finding was interpreted as a defense response to counteract the overproduction of reactive oxygen species in women with osteopenia. Results of the cross-sectional study indicated that bone resorption associated to osteopenia/osteoporosis does not pose a risk of lead toxicity in postmenopausal women exposed to background lead levels. However, results of the prospective suggest that three months of calcium supplementation contributed to a small, but significant increase of blood lead levels in postmenopausal women with bone disease. Although lead levels found in calcium supplements were below the limits established in the United States, it is important to regulate the allowed lead levels in calcium supplements in Brazil through of a specific legislation. A monitoring program of lead levels would also be important, because our results revealed that calcium supplements are a small lead source. Despite being a low lead source, it could cause deleterious effects, mainly in women in the postmenopausal.