Urine specific gravity (USG) thresholds are used in practice and research to determine hypohydration. However, some limited research has found that body size and body composition may impact USG, suggesting that fixed cutoffs may be insensitive. Cross-sectional data from 3,634 participants of the 2007–2008 National Health and Nutrition Examination Survey were analyzed. Along with USG, body mass index (BMI), estimated lean body mass (LBM), and dietary intake were quantified. Logistic regression models were used to evaluate whether higher quintiles of BMI and LBM were associated with elevated USG (USG ≥ 1.020 and ≥1.025) after accounting for dietary moisture and sodium. The USG (1.018 ± 0.0003 vs. 1.015 ± 0.0004); BMI (28.4 ± 0.2 vs. 28.0 ± 0.2 kg/m²); LBM (60.9 ± 0.3 vs. 42.2 ± 0.2 kg); dietary moisture (3,401 ± 92 vs. 2,759 ± 49 g/day); and dietary sodium (4,171 ± 85 vs. 2,959 ± 50) were greater in men than in women (p < .05). Men and women in the fifth quintiles of BMI or LBM (vs. Quintile 1) had greater odds (2.00–3.68, p < .05) of elevated USG. (The only exception was for the association between BMI and USG ≥ 1.025 in men.) Being in Quintile 4 of LBM or BMI (vs. Quintile 1) also tended to be associated with higher odds of elevated of USG, though this pattern was more consistent when using USG ≥ 1.020 than USG ≥ 1.025. In summary, BMI and LBM are associated with USG at the population level. These results affirm that USG depends on body size and composition and raise questions about using fixed USG thresholds for determining hypohydration, particularly for people in the upper quintiles of BMI and LBM.

尿比重 (USG) 阈值在实践和研究中用于确定脱水。然而，一些有限的研究发现，身体大小和身体成分可能会影响 USG，这表明固定截止值可能不敏感。分析了 2007-2008 年全国健康和营养检查调查的 3,634 名参与者的横断面数据。除了 USG，体重指数 (BMI)、估计的瘦体重 (LBM) 和膳食摄入量也被量化。在考虑膳食水分和钠后，逻辑回归模型用于评估较高的 BMI 和 LBM 五分位数是否与升高的 USG（USG ≥ 1.020 和 ≥1.025）相关。USG（1.018 ± 0.0003 与 1.015 ± 0.0004）；BMI (28.4 ± 0.2 与 28.0 ± 0.2 kg/m ²); LBM（60.9 ± 0.3 对 42.2 ± 0.2 公斤）；膳食水分（3,401 ± 92 对 2,759 ± 49 克/天）；男性的膳食钠含量（4,171 ± 85 vs. 2,959 ± 50）高于女性（p  < .05）。BMI 或 LBM 五分之一的男性和女性（与五分之一相比）的几率更大（2.00-3.68，p < .05) 升高的 USG。（唯一的例外是男性 BMI 和 USG ≥ 1.025 之间的关联。）处于 LBM 或 BMI 的五分位 4（与五分位 ​​1 相比）也往往与更高的 USG 升高几率相关，尽管这种模式更多使用 USG ≥ 1.020 时与使用 USG ≥ 1.025 时一致。总之，BMI 和 LBM 在人群水平上与 USG 相关。这些结果证实 USG 取决于身体大小和组成，并提出了使用固定 USG 阈值来确定缺水的问题，特别是对于 BMI 和 LBM 上五分之一的人。