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Original Research Communication |
1 From the Bone Metabolism Unit and the Cardiac Center, Creighton University, School of Medicine, Omaha.
See corresponding editorial on page 1073.
| ABSTRACT |
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Objective: The objective of this study was to examine the relation between alcohol intake and BMD, calcitropic hormones, calcium absorption, and other biochemical indexes of bone and mineral metabolism in elderly women.
Design: The results presented are derived from baseline observations of 489 elderly women (aged 6577 y) recruited for an osteoporosis study. The nondrinking group comprised 297 women and the drinking group comprised 148 women. Furthermore, the effect of different alcohol intakes (
28.6, >28.6 to
57.2, >57.2 to
142.9, and >142.9 g/wk) was studied.
Results: Women who consumed alcohol had significantly higher spine (10%), total body (4.5%), and midradius (6%) BMD than did nondrinkers. An alcohol intake >28.6 g/wk was associated with higher BMD; maximum effect was seen with an intake of >28.6 to
57.2 g/wk (16%, 12%, and 14% increase in spine, total body, and midradius BMD, respectively). There was a marked reduction in bone remodeling markers, serum osteocalcin, and the ratio of urinary cross-linked N-telopeptides of type 1 collagen to creatinine with alcohol consumption, suggesting that increased BMD with alcohol consumption could be due to reduced bone remodeling. Further, serum parathyroid hormone concentrations were significantly lower in alcohol drinkers than in nondrinkers and could be one of the causes of decreased bone resorption.
Conclusions: Moderate alcohol intake was associated with higher BMD in postmenopausal elderly women. The protective effect of alcohol may have been a result of lower bone remodeling due to reduced parathyroid hormone concentrations or factors such as increased estrogen concentrations.
Key Words: Alcohol bone mineral density BMD bone remodeling serum parathyroid hormone elderly women
| INTRODUCTION |
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Several studies showed that chronic alcoholism leads to osteopenia and increased incidence of skeletal fractures (35). Studies carried out to understand the underlying mechanism suggested that alcohol may have a direct effect on bone cells and an indirect or modulatory effect through mineral regulatory hormones (6, 7). Alcohol has been shown to decrease the bone formation rate by decreasing the osteoblast number, osteiod formation, and osteoblast proliferation (810). However, the effect of alcohol consumption on bone resorption has not been established clearly. Some histomorphometric studies showed increased bone resorption in moderate and heavy drinkers (10), whereas others found no effect (11). In addition, calcitropic hormones, including serum parathyroid hormone (PTH) and vitamin D metabolites, were reported to be altered by alcohol consumption (12, 13).
There are conflicting reports in the literature regarding the effect of moderate alcohol consumption on bone. Some researchers did not find a positive association between moderate alcohol intake and bone mineral density (BMD) (1421). However, recent studies, mostly in postmenopausal women, showed a positive correlation between BMD and moderate alcohol consumption (2228). Holbrook and Barrett-Connor (26) reported that social drinking is associated with higher BMD in both men and women. Similar observations were made in a study by Felson et al (27), who found that elderly women with an alcohol intake of
210 mL (7 oz)/wk had higher BMD than did nondrinkers at most sites tested. Fescaniks et al (28) also showed a linear increase in spine density over increasing categories of alcohol intake in postmenopausal women.
In the present study, we examined the effect of alcohol intake on BMD at baseline in elderly women recruited for a multicenter osteoporotic longitudinal study (Sites Testing Osteoporosis Prevention/Intervention; STOP/IT). In addition, we explored the possible mechanism of the effect of alcohol consumption by studying the biochemical variables related to bone and mineral metabolism.
| SUBJECTS AND METHODS |
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Dietary intake, alcohol consumption, and smoking history
Dietary intake data were collected with use of 7-d food diaries. Plastic food models (NASCO, Fort Artinson, WI) were used to help participants better estimate the quantities consumed. Average daily calcium, vitamin D, and caffeine intakes were calculated by using FOOD PROCESSOR II PLUS (version 5.1; Esha Research, Salem, OR).
The information on alcohol consumption and smoking history was obtained by a self-administered questionnaire. The information on frequency of smoking (ie, number of cigarettes/wk) and the quantity of beer, wine, and mixed drinks (or undiluted spirits) consumed per week was obtained. Total alcohol consumption was computed by multiplying the average amounts of actual alcohol content in the beer, wine, and mixed drinks by the amount drunk with use of the following conversion formula (27):
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On the basis of alcohol intake, the subjects were subdivided into alcohol drinkers and nondrinkers. Further, on the basis of the quantity of alcohol consumed, they were divided into 5 categories: nondrinkers,
28.6 g/wk, >28.6 to
57.2 g/wk, >57.2 to
142.9 g/wk, and >142.9 g/wk. Reproductive history, present use of medications, and use of vitamin and mineral supplements were also assessed by a questionnaire. The information on past estrogen use and history of fractures was also obtained from the subjects.
Calcium absorption test
Calcium absorption was measured in a fasting state by oral administration of 18.5 x 104 Bq (5 µCi) 45Ca (Amersham, Arlington Heights, IL) in 100 mg CaCl2 carrier given in a total volume of 250 mL distilled water (29). A blood sample was collected 2 h after the oral dose. 45Ca activity was counted in 2 mL serum with a 1900 CA Tricarb Liquid scintillation analyzer (Packard Instrument, Meriden, CT). A parallel standard taken from the patient's dose before ingestion was counted at the same time as the sample. Calcium absorption was expressed as percentage of the actual dose/L blood (% AD/L) and corrected for body weight.
Biochemical analysis
Fasting blood and spot urine samples were collected before the calcium absorption test; a 24-h urine sample was also obtained from the subjects. Blood specimens were allowed to clot and were then centrifuged at 2056 x g for 15 min at 4°C to separate serum. All samples were stored frozen at 70°C until analyzed.
Serum and urine chemistry measurements
All serum and urine measurements were made with fresh samples. Serum ionized calcium and total calcium and creatinine in serum and urine samples (both spot and 24-h) were determined by using automated procedures (Nova Nucleus Chemistry Analyzer, Waltham, MA). Serum albumin, alanine aminotransferase (ALT), and alkaline phosphatase were measured by using automated procedures (Technicon SMAC Analyzer; Technicon Corp, Tarrytown, NY).
Serum calciotropic hormones
Serum 25-hydroxyvitamin D [calcidiol, or 25(OH)D] was measured with use of a competitive protein binding assay (30) after extraction and purification of serum on Sep-Pak cartridges (Waters Associates, Milford, MA) (31). The limit of detection was 12.5 mmol/L (5 µg/L) and the interassay variation was 5%. Serum 1,25-dihydroxyvitamin D [calcitriol, or 1,25(OH)2D] was measured with a nonequilibrium radioreceptor assay (Incstar Corp, Stillwater, MN) by using calf thymus receptor. The samples were extracted and purified before assay on nonpolar C18OH octadecyl silanol silica cartridges (32, 33). The limit of detection for the assay was 12 pmol/L (5 ng/L) and the interassay variation was 10%. Allegro immunoradiometric assay (Nichols Institute, San Juan Capistrano, CA) was used to measure serum intact PTH (iPTH) (34). The limit of detection for the assay was 1 ng/L (1 pg/mL) and the interassay variation was 5%.
Bone markers
Serum osteocalcin was measured by using radioimmunoassay (Incstar Corp). The limit of detection for the assay was 0.78 µg/L (0.78 ng/mL) and the interassay variation was 5%. Urine collagen crosslinks were measured by enzyme-linked immunosorbent assay (Osteomark International, Seattle) as N-telopeptides, a specific marker for bone type I collagen [expressed as nmol bone collagen equivalents (BCE)/mmol of creatinine].
Bone mineral density
BMD at hip (femoral neck, trochanter, and Ward's triangle), whole body, lumbar spine (vertebrae 12), and midradius was measured by dual-energy X-ray absorptiometry (model DPX-L; Lunar Corp, Madison, WI) by using standardized protocols for uniform subjects positioning, scan mode, and scan analysis. Hip and spine scans were performed in duplicate and the average value computed was used for the analysis. Of all the hip measurements, only the femoral neck BMD is reported because measurements at all the sites of hip showed a similar trend.
Statistical analysis
Data were analyzed with SPSS for WINDOWS (version 8.0; SPSS Inc, Chicago). BMD measurements of nondrinkers and drinkers were compared by analysis of covariance (ANCOVA) after adjustment for smoking status, past estrogen use, and other significantly correlated covariates identified by correlation analysis. A similar analysis was done between nondrinkers and consumers of various categories of alcohol intake. We used a Bonferroni multiple comparison test adjusted only for comparisons of interest (ie, the 4 subgroups of alcohol compared with nondrinkers) to determine post hoc significance between the various categories of alcohol intake. Measurements of calcitropic hormones, bone markers, and serum chemistry were analyzed similarly.
Pearson's correlation coefficients were calculated to determine whether the BMD measurements at various sites, calcitropic hormones, bone markers, and serum chemistry measurements were related to age, height, weight, age at menopause, dietary calcium, protein, vitamin D, and caffeine intakes. Covariates were considered significant if P was <0.05. Of all the covariates, weight was significantly correlated with most of the variables, whereas varied results were obtained for the other covariates. For each dependent variable in the ANCOVA, only significant (P < 0.05) covariates were included in the model. The data are presented as adjusted means and SEMs.
Of the total 445 subjects considered for the analysis, 88 had no information available for age at menopause. Years since menopause correlated significantly only with BMD measurements at spine and total body. Additional analysis that included years since menopause as a covariate for BMD measurements at spine and total body did not significantly affect the direction of the differences. Therefore, the results of BMD measurements for spine and total body, without correction for years since menopause, are presented.
| RESULTS |
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142.9 g/wk had significantly lower body weights than did nondrinkers. Although caffeine intake was marginally higher in all categories of drinkers than in nondrinkers, the values were not significantly different. The mean (±SEM) age at menopause was also significantly higher in drinkers (49.2 ± 0.79 y) than in nondrinkers (47.4 ± 0.42 y). When consumers of different categories of alcohol intake were compared with nondrinkers, none of them were significantly different from nondrinkers with regard to the age at menopause. Subjects in all the categories of alcohol intake were also not significantly different from nondrinkers with regard to age, height, or dietary calcium, vitamin D, protein, and energy intakes; 11.5% of nondrinkers and 18.2% of drinkers were current smokers. The percentage of current smokers in the alcohol intake categories of >57.2 to
142.9 and >142.9 g/wk was higher: 23% and 30% of women in these categories, respectively, were current smokers. Eighteen percent of both alcohol drinkers and nondrinkers gave a history of estrogen use of >1 y. The distribution of percentage of past estrogen users was not significantly different between various categories of alcohol intake. Forty-seven percent of nondrinkers and 48% of drinkers had a history of fractures. The rate of history of fractures of consumers of various categories of alcohol intake was not significantly different from that of nondrinkers (nondrinkers, 47.3%;
28.6 g/wk, 44.3%; >28.6 to
57.2 g/wk, 51.5%; >57.2 to
142.9 g/wk, 42.3%; and >142.9 g/wk, 55%; Pearson's chi-square, P < 0.87).
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57.2 g/wk had the highest lumbar spine, total body, and midradius BMD compared with nondrinkers; the differences (all significant) were 16%, 12%, and 14%, respectively, between the 2 groups. Even at the femoral neck, this group of women tended to have higher BMD (6%), but this difference was not significant. Consumption of >57.2 to
142.9 and >142.9 g/wk also tended to increase the BMD at all the sites measured. However, only lumbar spine density (15%) and total body density (5.5%) of subjects in the category of >142.9 g/wk were significantly higher than that of nondrinkers.
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57.2 g/wk than in nondrinkers, whereas in other categories of alcohol intake the values were not significantly different from those of nondrinkers. Serum calcium, phosphorus, alkaline phosphatase, and albumin were not significantly different between consumers of different categories of alcohol intake and nondrinkers, except for alkaline phosphatase, which was significantly higher in subjects with an alcohol intake
28.6 g/wk than in nondrinkers. The liver enzyme ALT was not significantly different between the alcohol drinkers and the nondrinkers (0.5 ± 0.03 compared with 0.47 ± 0.01 µkat/L) and between the consumers of different categories of alcohol intake and the nondrinkers (nondrinkers, 0.47 ± 0.01;
28.6 g/wk, 0.49 ± 0.03; >28.6 to
57.2 g/wk, 0.45 ± 0.02; >57.2 to
142.9 g/wk, 0.49 ± 0.03; and >142.9 g/wk, 0.54 ± 0.04 µkat/L).
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When the subjects were categorized into different levels of alcohol intake, serum 25(OH)D tended to be lower in subjects with an alcohol intake of >57.2 to
142.9 g/wk than in nondrinkers (Table 2
). Serum 25(OH)D in other categories of alcohol intake was not significantly different from that of nondrinkers. Women with alcohol intakes of >28.6 to
57.2, >57.2 to
142.9, and >142.9 g/wk had lower serum PTH concentrations than did nondrinkers, but only in women with an alcohol intake >28.6 to
57.2 g/wk were the values significantly lower (Figure 2
). Serum 1,25(OH)2D concentrations were not significantly different between drinkers and nondrinkers (Table 2
) and the amount of alcohol consumed did not significantly influence the serum 1,25(OH)2D concentrations.
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57.2 g/wk or an intake of >57.2 to
142.9 g/wk had significantly lower serum osteocalcin concentrations (31% and 33%, respectively) than did nondrinkers. Women in alcohol intake categories of >28.6 to
57.2, >57.2 to
142.9, and >142.9 g/wk had lower NTX:Cr (38%, 27%, and 19%, respectively) than did nondrinkers, although not significantly so. Correlations were run between bone markers, serum PTH, and BMD for the entire study population. A significant positive correlation (although not a very strong one) was observed between PTH and bone remodeling markers (PTH and serum osteocalcin, r = 0.211, P < 0.001; PTH and NTX:Cr, r = 0.11, P < 0.05). There were significant negative correlations (albeit weak) between bone remodeling markers and BMD (total body BMD and serum osteocalcin, r = -0.30, P < 0.001; total body BMD and NTX:Cr, r = -0.32, P < 0.001; spine BMD and serum osteocalcin, r = -0.141, P < 0.01; spine BMD and NTX:Cr, r = -0.140, P < 0.01).
The fasting ratio of urinary calcium to creatinine (Ca:Cr) (Table 2
) was not significantly different between drinkers and nondrinkers. However, women with an alcohol intake of >28.6 to
57.2 g/wk had significantly higher excretion of calcium in urine than did nondrinkers (Table 2
). Fasting Ca:Cr in other categories of alcohol intake was not significantly different from that of nondrinkers.
| DISCUSSION |
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Laitinen et al (22) first reported a positive correlation between alcohol intake and BMD, with a 12%, 15%, and 9% increase at lumbar spine, Ward's triangle, and femoral neck, respectively, in alcohol drinkers; spine and Ward's triangle values were significant. Feskanich et al (28) observed that women who consumed
75 g alcohol/wk had significantly higher lumbar spine BMD (12%) than did nondrinking women. They also observed a linear increase in spinal BMD over increasing alcohol intakes. However, a similar effect was not found at femoral neck and total hip. Holbrook and Barrett-Connor (26), in a prospective study of men and women, observed that alcohol consumption was associated with an increase in BMD. They reported significant increases in BMD at femur in men and at spine and midradius in women with increasing alcohol intakes (10% increase with alcohol intake of 120 g/wk). In the Framingham study, Felson et al (27) observed that women who drank
200 g alcohol/wk had higher BMD than did those who drank <200 g. They reported 7.5%, 6%, and 4% higher spine, radius, and femoral neck BMD, respectively, in alcohol drinkers; only spine and radius BMD changes were significant. These authors made similar observations in men with high alcohol intakes, although the results were not significant.
In the present study, we observed a significant positive effect of alcohol consumption >28.6 g/wk, which is lower than that reported by earlier researchers. Maximum benefit of alcohol consumption was noted at an intake of >28.6 to
57.2 g/wk. Intakes of >57.2 to
142.9 and >142.9 g/wk also increased BMD but the effect was less than that seen with an intake of >28.6 to
57.2 g/wk. As observed by others, the effect of alcohol was seen primarily at the lumbar spine (ranging from 7% to 16% for various alcohol intakes). In addition, in our study, increasing alcohol intakes increased BMD significantly at the midradius (814% for various alcohol intakes) and total body (512% at different alcohol intakes). Although femur density was increased by alcohol intake, the effect was not significant, as seen by earlier researchers.
The higher BMD seen in alcohol drinkers in our study could be due mainly to reduction in bone remodeling, as evidenced by the decrease in bone resorption markers, NTX:Cr (1938% for various alcohol intake categories) and serum osteocalcin (2231% for various alcohol intake categories). This is the first study that provides direct evidence of decreased bone remodeling markers with moderate alcohol consumption in postmenopausal elderly women.
Although serum osteocalcin is secreted by osteoblasts and is a marker of bone formation, it correlates highly with resorption because formation and resorption are coupled. Serum osteocalcin is increased in diseases with accelerated bone turnover rate (35, 36). In fact, in our study we observed a significant positive correlation between serum osteocalcin and urinary N-telopeptides.
We observed decreased serum PTH concentrations with intakes of alcohol >28.6 g/wk, which could be a cause of the reduced bone resorption. Decreased secretion of PTH hormone was observed with short-term alcohol consumption (37). In addition, Diez et al (38) reported decreased PTH after adjustment for age and sex in 20 men and 6 women with daily intakes of
150 g alcohol for
8 y. In our study, we observed a significant positive correlation between serum PTH and bone markers. The bone markers were in turn negatively correlated with BMD. This further corroborates our notion that the reduced bone remodeling may be due to decreased PTH concentrations.
Other causes of increases in BMD with alcohol consumption that have been suggested are increased serum calcitonin concentrations and increased estrogen concentration. Alcohol is known to stimulate calcitonin production (13), which increases the vertebral BMD without much effect on femoral sites (39, 40). Alternatively, elevation of estrogen concentrations by moderate alcohol consumption may help protect the skeleton. Higher estrogen concentrations have been found in postmenopausal women who consume alcohol (4143). Thus, the effect of alcohol could also be explained by hormonal factors. The age at menopause in our study subjects was significantly higher in alcohol drinkers than in nondrinkers. Early menopause in women is associated with quantitatively higher bone loss than in women with late-onset menopause (44). It could be argued that the late menopause in alcohol consumers is one of the reasons for the higher BMD observed in these women. However, even after adjustment for age at menopause, alcohol consumption was associated with higher BMD, suggesting that the effect of alcohol was not due to delayed menopause.
In the present study, serum 25(OH)D was found to be marginally lower in subjects consuming >57.2 to
142.9 g alcohol/wk. However, serum 1,25(OH)2D concentrations remained normal in these subjects. A decreased concentration of total 25(OH)D with normal free 25(OH)D has been reported in chronic alcoholism (45). The effect of alcohol intakes of >28.6 to
57.2 g/wk, which is a moderate range, on calcitropic hormones tends to be similar to that seen in chronic alcoholism, although it is marginal. The reason for this observation is not clear. To our knowledge there are no reports of the effect of moderate alcohol consumption on calcitropic hormones in postmenopausal women.
In conclusion, we report a positive association between alcohol consumption and BMD. We also provide substantial evidence indicating that the increase in BMD by alcohol in our elderly population was due mainly to a decrease in bone remodeling. The decreased remodeling may have been due to lowered serum PTH concentrations or may have been mediated through hormonal effects such as higher serum calcitonin concentrations or estrogen concentrations. Although mild to moderate alcohol intake has a protective effect on bone, these results should be viewed with caution because alcohol abuse has apparent untoward effects on bone mineral metabolism.
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