Association between phase angle and all-cause mortality in adults aged 18-49 years: NHANES 1999-2004

Phase angle (PhA) is an indicator of nutritional status. The association between PhA and all-cause mortality has been confirmed in older adults, but no relevant studies have been conducted in adults aged 18-49 years. This study aimed to investigate the relationship between PhA and all-cause mortality in adults aged 18-49 years. Our study included 6338 adults aged 18-49 from the National Health and Nutrition Examination Survey (1999-2004). Kaplan-Meier (KM) curve, multiple Cox regression and stratified analyses were performed. These adults were divided into two groups based on the median PhA value (the low PhA group: PhA < 6.96°; the high PhA group: PhA ≥ 6.96°). During a median follow-up of 214 months, 307 all-cause deaths were recorded. The all-cause mortality rate was 5.07% in the low PhA group and 3.98% in the high PhA group. After full adjustment, a higher PhA value was significantly associated with reduced risk of all-cause mortality (HR = 0.73,95CI%:0.59-0.91, P = 0.005). Similarly, compared with those in the low PhA group, individuals in the high PhA group had a lower risk of all-cause mortality (HR = 0.67, 95% CI 0.46-0.98, P = 0.041). There was an interaction between smoking status and PhA (P for interaction = 0.029), with a statistically significant negative association between PhA and all-cause mortality in the non-smokers (HR:0.62, 95%CI:0.53-0.88, P = 0.003). In conclusion, there was a significant negative association between PhA and all-cause mortality in adults aged 18-49 years. The negative association was stronger in non-smokers.