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Serum bicarbonate and bone mineral density in US adults.

BACKGROUND
Chronic metabolic acidosis leads to bone mineral loss and results in lower bone mineral density (BMD), which is a risk factor for osteoporosis-related fractures. The effect of low-level metabolic acidosis on bone density in the general population is unknown.


STUDY DESIGN
Cross-sectional study.


SETTING & PARTICIPANTS
9,724 nationally representative adults 20 years or older in NHANES (National Health and Nutrition Examination Survey) 1999-2004.


FACTOR
Serum bicarbonate level.


OUTCOMES
Lumbar and total BMD, as well as low lumbar and total bone mass, defined as 1.0 SD below the sex-specific mean value of young adults.


MEASUREMENTS
BMD was measured by dual-energy x-ray absorptiometry and serum bicarbonate was measured in all participants.


RESULTS
Both men and women with lower serum bicarbonate levels were more likely to be current smokers and had higher body mass index and estimated net endogenous acid production. There was a significant linear trend across quartiles of serum bicarbonate with lumbar BMD in the total population, as well as in sex-specific models (P=0.02 for all 3 models, P=0.1 for interaction). For total BMD, a significant association was seen with serum bicarbonate level for women but not men (P=0.02 and P=0.1, respectively; P=0.8 for interaction), and a significant association was seen for postmenopausal women but not premenopausal women (P=0.02 and P=0.2, respectively; P=0.5 for interaction). Compared with women with serum bicarbonate levels <24mEq/L, those with serum bicarbonate levels ≥27mEq/L had 0.018-g/cm(2) higher total BMD (95% CI, 0.004-0.032; P=0.01) and 31% lower odds of having low total bone mass (OR, 0.68; 95% CI, 0.46-0.99; P=0.049).


LIMITATIONS
Cross-sectional study using a single measurement of serum bicarbonate. Subgroup differences are not definitive.


CONCLUSIONS
Lower serum bicarbonate levels are associated with lower BMD in US adults. Further studies should examine whether serum bicarbonate levels should be incorporated into the diagnostic assessment and management of osteoporosis.