High dietary phosphorus intake is associated with all-cause mortality: results from NHANES III

Abstract

Background: Elevated serum phosphorus is associated with all-cause mortality, but little is known about risk associated with dietary phosphorus intake.

Objective: We investigated the association between phosphorus intake and mortality in a prospective cohort of healthy US adults (NHANES III; 1998-1994).

Design: Study participants were 9686 nonpregnant adults aged 20-80 y without diabetes, cancer, or kidney or cardiovascular disease. Exposure to dietary phosphorus, which was assessed by using a 24-h dietary recall, was expressed as the absolute intake and phosphorus density (phosphorus intake divided by energy intake). All-cause and cardiovascular mortality was assessed through 31 December 2006.

Results: Median phosphorus intake was 1166 mg/d (IQR: 823-1610 mg/d); median phosphorus density was 0.58 mg/kcal (0.48-0.70 mg/kcal). Individuals who consumed more phosphorus-dense diets were older, were less often African American, and led healthier lifestyles (smoking, physical activity, and Healthy Eating Index). In analyses adjusted for demographics, cardiovascular risk factors, kidney function, and energy intake, higher phosphorus intake was associated with higher all-cause mortality in individuals who consumed >1400 mg/d [adjusted HR (95% CI): 2.23 (1.09, 4.5) per 1-unit increase in ln(phosphorus intake); P = 0.03]. At <1400 mg/d, there was no association. A similar association was seen between higher phosphorus density and all-cause mortality at a phosphorus density amount >0.35 mg/kcal [adjusted HR (95% CI): 2.27 (1.19, 4.33) per 0.1-mg/kcal increase in phosphorus density; P = 0.01]. At <0.35 mg/kcal (approximately the fifth percentile), lower phosphorus density was associated with increased mortality risk. Phosphorus density was associated with cardiovascular mortality [adjusted HR (95% CI): 3.39 (1.43, 8.02) per 0.1 mg/kcal at >0.35 mg/kcal; P = 0.01], whereas no association was shown in analyses with phosphorus intake. Results were similar by subgroups of diet quality and in analyses adjusted for sodium and saturated fat intakes.

Conclusions: High phosphorus intake is associated with increased mortality in a healthy US population. Because of current patterns in phosphorus consumption in US adults, these findings may have important public health implications.

FIGURE 1.

Distribution and adjusted HRs (95% CIs) of death by absolute phosphorus intake. Cox proportional hazards regression was used to estimate HRs of mortality by absolute phosphorus intake by using linear splines with a knot at 1400 mg/d adjusted for age, sex, race, ethnicity, poverty:income ratio, total energy intake, BMI, systolic blood pressure, current and former smoking, physical activity, non–HDL cholesterol, log albumin:creatinine ratio, estimated glomerular filtration rate, and low vitamin D concentration. Values were centered at 700 mg/d, and the graph is truncated at 200 and 4000 mg/d for ease of presentation. *The Recommended Dietary Allowance (700 mg/d) represents the daily dietary intake of phosphorus considered sufficient by the Food and Nutrition Board to meet requirements for nearly all (97.5%) healthy adults; **the tolerable upper limit (4000 mg/d) is the highest average phosphorus intake that is likely to pose no adverse health effects to almost all individuals in a general population (1).

FIGURE 2.

Distribution and adjusted HRs (95% CIs) of death by phosphorus density. Cox proportional hazards regression was used to estimate HRs of mortality by phosphorus density by using linear splines with a knot at 0.35 mg/kcal adjusted for age, sex, race, ethnicity, poverty:income ratio, total energy intake, BMI, systolic blood pressure, current and former smoking, physical activity, non–HDL cholesterol, albumin:creatinine ratio, estimated glomerular filtration rate, and low vitamin D concentration. Values were centered at 0.35 mg/kcal, which corresponded to 700 mg/d for a 2000-kcal/d diet, and the graph is truncated at 0.25 and 1.5 mg/kcal for ease of presentation.