Dietary phosphorus, blood pressure, and incidence of hypertension in the atherosclerosis risk in communities study and the multi-ethnic study of atherosclerosis

Potential health concerns of dietary phosphorus: cancer, obesity, and hypertension

Adult Americans typically consume on average 1400 mg, or more, of phosphorus (P) daily in meals, which almost doubles the recommended dietary allowance. After a meal phosphorus is rapidly absorbed at a high efficiency and hormonal mechanisms act swiftly to maintain the serum inorganic phosphate (Pi) concentration within fairly narrow limits. Both parathyroid hormone (PTH) and fibroblast growth factor-23 (FGF-23) reduce serum phosphate during postprandial periods through homeostatic actions on the kidney. However, it is speculated that exposure of cells to a brief high-serum Pi concentration may signal alterations in cell functions that lead to deleterious effects. Elevation of serum FGF-23 or PTH may also be harmful to specific cell types. Examples of possible adverse health effects include cancer, obesity, and hypertension. Here I review potential mechanisms through which high-P intake may contribute to cell metabolic abnormalities and the development of chronic disease; high-dietary phosphorus, especially from foods processed with phosphate salts, may be associated with these chronic diseases. Further investigation is needed to establish the significance of high-phosphate diets within a large segment of the U.S. population with normal renal function.

Public health impact of dietary phosphorus excess on bone and cardiovascular health in the general population

This review explores the potential adverse impact of the increasing phosphorus content in the American diet on renal, cardiovascular, and bone health of the general population. Increasingly, studies show that phosphorus intakes in excess of the nutrient needs of a healthy population may significantly disrupt the hormonal regulation of phosphate, calcium, and vitamin D, which contributes to disordered mineral metabolism, vascular calcification, impaired kidney function, and bone loss. Moreover, large epidemiologic studies suggest that mild elevations of serum phosphate within the normal range are associated with cardiovascular disease (CVD) risk in healthy populations without evidence of kidney disease. However, few studies linked high dietary phosphorus intake to mild changes in serum phosphate because of the nature of the study design and inaccuracies in the nutrient composition databases. Although phosphorus is an essential nutrient, in excess it could be linked to tissue damage by a variety of mechanisms involved in the endocrine regulation of extracellular phosphate, specifically the secretion and action of fibroblast growth factor 23 and parathyroid hormone. Disordered regulation of these hormones by high dietary phosphorus may be key factors contributing to renal failure, CVD, and osteoporosis. Although systematically underestimated in national surveys, phosphorus intake seemingly continues to increase as a result of the growing consumption of highly processed foods, especially restaurant meals, fast foods, and convenience foods. The increased cumulative use of ingredients containing phosphorus in food processing merits further study given what is now being shown about the potential toxicity of phosphorus intake when it exceeds nutrient needs.

Metabolomics and incident hypertension among blacks: the atherosclerosis risk in communities study

Development of hypertension is influenced by genes, environmental effects, and their interactions, and the human metabolome is a measurable manifestation of gene-environment interaction. We explored the metabolomic antecedents of developing incident hypertension in a sample of blacks, a population with a high prevalence of hypertension and its comorbidities. We examined 896 black normotensives (565 women; aged, 45-64 years) from the Atherosclerosis Risk in Communities study, whose metabolome was measured in serum collected at the baseline examination and analyzed by high-throughput methods. The analyses presented here focus on 204 stably measured metabolites during a period of 4 to 6 weeks. Weibull parametric models considering interval censored data were used to assess the hazard ratio for incident hypertension. We used a modified Bonferroni correction accounting for the correlations among metabolites to define a threshold for statistical significance (P<3.9 × 10(-4)). During 10 years of follow-up, 38% of baseline normotensives developed hypertension (n=344). With adjustment for traditional risk factors and estimated glomerular filtration rate, each +1SD difference in baseline 4-hydroxyhippurate, a product of gut microbial fermentation, was associated with 17% higher risk of hypertension (P=2.5 × 10(-4)), which remained significant after adjusting for both baseline systolic and diastolic blood pressure (P=3.8 × 10(-4)). After principal component analyses, a sex steroids pattern was significantly associated with risk of incident hypertension (highest versus lowest quintile hazard ratio, 1.72; 95% confidence interval, 1.05-2.82; P for trend, 0.03), and stratified analyses suggested that this association was consistent in both sexes. Metabolomic analyses identify novel pathways in the pathogenesis of hypertension.

Utilizing harmonization and common surveillance methods to consolidate 4 cohorts: the Western Alaska Tribal Collaborative for Health (WATCH) study

BACKGROUND

According to health status reports, chronic disease prevalence appears to be rising in western Alaska Native (AN) people, and accurate population-based data are needed. Four cohort studies of western AN people were conducted in the Norton Sound and Yukon-Kuskokwim regions, but none have been large enough to allow reliable estimates of rates of chronic diseases and evaluate their risk factors.

OBJECTIVE

In this article, the methods used to combine 4 major cohort studies of rural western AN people are described and the benefits and challenges encountered in combining data and standardizing surveillance methods for these studies are discussed.

DESIGN

Tribal permission was obtained for each cohort study and the consolidated study. Data from baseline exams were directly combined or harmonized into new variables. Common surveillance methods were developed and implemented to identify incidence and risk factors for cardiovascular disease (CVD) events and type 2 diabetes.

RESULTS

A cohort of 4,569 western AN participants (2,116 men and 2,453 women), aged 18-95 years, was established to study CVD and diabetes prevalence. Prospective surveillance data over an average 6.7-year follow-up can now be used to study CVD and diabetes incidence and associated risk factors in a subset of 2,754 western AN participants (1,218 men and 1,536 women) who consented to initial surveillance.

CONCLUSIONS

The combined cohort provides statistical power to examine incidence rates and risk factors for CVD and diabetes and allows for analyses by geographic region. The data can be used to develop intervention programmes in these populations and others.

Contributions to total phosphorus intake: all sources considered

High serum phosphorus is linked to poor health outcome and mortality in chronic kidney disease (CKD) patients before or after the initiation of dialysis. Dietary intake of phosphorus, a major determinant of serum phosphorus, seems to be systematically underestimated using the available software tools and generalized nutrient content databases. Several sources of dietary phosphorus including the addition of phosphorus ingredients in food processing, and phosphorus content of vitamin and mineral supplements and commonly used over-the-counter or prescription medications are not fully accounted for by the nutrient content databases and software programs in current clinical use or used in large population studies. In this review, we explore the many unknown sources of phosphorus in the food supply to identify all possible contributors to total phosphorus intake of Americans that have escaped inclusion in past intake estimates. Our goal is to help delineate areas for future interventions that will enable tighter control of dietary phosphorus intake, a critical factor to maintaining health and quality of life in CKD and dialysis patients.

Dietary intake of saturated fat by food source and incident cardiovascular disease: the Multi-Ethnic Study of Atherosclerosis

BACKGROUND

Although dietary recommendations have focused on restricting saturated fat (SF) consumption to reduce cardiovascular disease (CVD) risk, evidence from prospective studies has not supported a strong link between total SF intake and CVD events. An understanding of whether food sources of SF influence these relations may provide new insights.

OBJECTIVE

We investigated the association of SF consumption from different food sources and the incidence of CVD events in a multiethnic population.

DESIGN

Participants who were 45-84 y old at baseline (n = 5209) were followed from 2000 to 2010. Diet was assessed by using a 120-item food-frequency questionnaire. CVD incidence (316 cases) was assessed during follow-up visits.

RESULTS

After adjustment for demographics, lifestyle, and dietary confounders, a higher intake of dairy SF was associated with lower CVD risk [HR (95% CI) for +5 g/d and +5% of energy from dairy SF: 0.79 (0.68, 0.92) and 0.62 (0.47, 0.82), respectively]. In contrast, a higher intake of meat SF was associated with greater CVD risk [HR (95% CI) for +5 g/d and a +5% of energy from meat SF: 1.26 (1.02, 1.54) and 1.48 (0.98, 2.23), respectively]. The substitution of 2% of energy from meat SF with energy from dairy SF was associated with a 25% lower CVD risk [HR (95% CI): 0.75 (0.63, 0.91)]. No associations were observed between plant or butter SF and CVD risk, but ranges of intakes were narrow.

CONCLUSION

Associations of SF with health may depend on food-specific fatty acids or other nutrient constituents in foods that contain SF, in addition to SF.

Relations between dairy food intake and arterial stiffness: pulse wave velocity and pulse pressure

Modifiable risk factors, such as diet, are becomingly increasingly important in the management of cardiovascular disease, one of the greatest major causes of death and disease burden. Few studies have examined the role of diet as a possible means of reducing arterial stiffness, as measured by pulse wave velocity, an independent predictor of cardiovascular events and all-cause mortality. The aim of this study was to investigate whether dairy food intake is associated with measures of arterial stiffness, including carotid-femoral pulse wave velocity and pulse pressure. A cross-sectional analysis of a subset of the Maine-Syracuse Longitudinal Study sample was performed. A linear decrease in pulse wave velocity was observed across increasing intakes of dairy food consumption (ranging from never/rarely to daily dairy food intake). The negative linear relationship between pulse wave velocity and intake of dairy food was independent of demographic variables, other cardiovascular disease risk factors, and nutrition variables. The pattern of results was very similar for pulse pressure, whereas no association between dairy food intake and lipid levels was found. Further intervention studies are needed to ascertain whether dairy food intake may be an appropriate dietary intervention for the attenuation of age-related arterial stiffening and reduction of cardiovascular disease risk.

Relation between dairy food intake and cognitive function: The Maine-Syracuse Longitudinal Study

Diet modification to alter the course of age-related cognitive decline is becoming increasingly important. Few observational findings suggest that dairy food intake may be positively related to cognitive function, but research in this novel area is limited. The aim of this study was to investigate whether dairy food intake is associated with cognitive function, before and after adjustment for cardiovascular, lifestyle and dietary factors. To do this, a cross-sectional analyses of a subset of the community-based Maine-Syracuse Longitudinal Study (MSLS) sample (N = 972) was undertaken. It was determined that participants who consumed dairy products at least once per day had significantly higher scores on multiple domains of cognitive function compared with those who never or rarely consumed dairy foods, adjusting for cardiovascular risk factors, lifestyle and dietary factors. Frequent dairy food intake is associated with better cognitive performance but underlying causal mechanisms are still to be determined.

Diet and Alzheimer's disease risk factors or prevention: the current evidence

Preventing or postponing the onset of Alzheimer's disease (AD) and delaying or slowing its progression would lead to a consequent improvement of health status and quality of life in older age. Elevated saturated fatty acids could have negative effects on age-related cognitive decline and mild cognitive impairment (MCI). Furthermore, at present, epidemiological evidence suggests a possible association between fish consumption, monounsaturated fatty acids and polyunsaturated fatty acids (PUFA; in particular, n-3 PUFA) and a reduced risk of cognitive decline and dementia. Poorer cognitive function and an increased risk of vascular dementia (VaD) were found to be associated with a lower consumption of milk or dairy products. However, the consumption of whole-fat dairy products may be associated with cognitive decline in the elderly. Light-to-moderate alcohol use may be associated with a reduced risk of incident dementia and AD, while for VaD, cognitive decline and predementia syndromes, the current evidence is only suggestive of a protective effect. The limited epidemiological evidence available on fruit and vegetable consumption and cognition generally supports a protective role of these macronutrients against cognitive decline, dementia and AD. Only recently, higher adherence to a Mediterranean-type diet was associated with decreased cognitive decline, although the Mediterranean diet (MeDi) combines several foods, micro- and macro-nutrients already separately proposed as potential protective factors against dementia and predementia syndromes. In fact, recent prospective studies provided evidence that higher adherence to a Mediterranean-type diet could be associated with slower cognitive decline, reduced risk of progression from MCI to AD, reduced risk of AD and a decreased all-cause mortality in AD patients. These findings suggested that adherence to the MeDi may affect not only the risk of AD, but also of predementia syndromes and their progression to overt dementia. Based on the current evidence concerning these factors, no definitive dietary recommendations are possible. However, following dietary advice for lowering the risk of cardiovascular and metabolic disorders, high levels of consumption of fats from fish, vegetable oils, nonstarchy vegetables, low glycemic index fruits and a diet low in foods with added sugars and with moderate wine intake should be encouraged. Hopefully this will open new opportunities for the prevention and management of dementia and AD.

Association of dietary sodium and potassium intakes with albuminuria in normal-weight, overweight, and obese participants in the Reasons for Geographic and Racial Differences in Stroke (REGARDS) Study

BACKGROUND

Among obese adults, sodium intake has been associated with cardiovascular disease. Few data are available on sodium intake and albuminuria, a marker of kidney damage and risk factor for cardiovascular disease.

OBJECTIVE

We examined the relation between dietary sodium and potassium intakes and the ratio of sodium to potassium (Na/K) with albuminuria by BMI in the Reasons for Geographic and Racial Differences in Stroke (REGARDS) Study (n = 30,239 adults aged ≥45 y).

DESIGN

A modified Block 98 food-frequency questionnaire was used for dietary assessment in 21,636 participants, and nutritional variables were categorized by sex-specific quintiles. Normal weight, overweight, and obese were defined as BMI (in kg/m(2)) categories of 18.5-24.9, 25-29.9, and ≥30, respectively. Albuminuria was defined as a ratio (mg/g) of urinary albumin to creatinine of ≥30.

RESULTS

The prevalences of albuminuria were 11.5%, 11.6%, and 16.0% in normal-weight, overweight, and obese participants, respectively. The multivariable-adjusted ORs for albuminuria in a comparison of the highest with the lowest quintile of Na/K intake (≥1.12 to <0.70 for men and ≥1.07 to <0.62 for women) were 0.89 (95% CI: 0.65, 1.22), 1.08 (95% CI: 0.85, 1.36), and 1.28 (95% CI: 1.02, 1.61) in normal-weight, overweight, and obese participants, respectively. The highest quintile of dietary sodium was associated with an increased OR for albuminuria in obese participants (OR: 1.44; 95% CI: 1.00, 2.07) but not in normal-weight or overweight participants. Dietary potassium was not associated with albuminuria.

CONCLUSION

In obese adults, higher dietary Na/K and sodium intakes were associated with albuminuria.

Phosphate: the new cholesterol? The role of the phosphate axis in non-uremic vascular disease

Higher serum phosphate levels within the normal range are associated with substantially increased risk of cardiovascular disease events. Whether this reflects a causative relationship is unknown. Phosphate-responsive hormones (fibroblast growth factor-23, parathyroid hormone and calcitriol) are also predictors of cardiovascular mortality in populations without kidney disease or recognised disturbances of bone mineral metabolism. The high bioavailable phosphate content of Western diets may contribute to this apparent discrepancy between 'normal' and optimal phosphate axis parameters. Although uremic hyperphosphatemia is recognised to cause vascular medial calcification, this does not readily explain the association of higher-normal phosphate with common athero-occlusive phenomena. The phosphate axis may in fact play a role in atherogenesis; observational data link higher levels of phosphate and fibroblast growth factor-23 with coronary atheroma burden, whilst dietary phosphate supplementation accelerates atherosclerosis in a mouse model. In vitro studies show adverse effects of phosphate increases on both vascular smooth muscle cells and endothelium, though these observations have not yet been extended to phosphate increments within the normal range. Receptors for phosphate-responsive hormones are present throughout the cardiovascular system and may mediate atherogenic effects. Since interventions are already available to manipulate the phosphate axis, this is an important issue. If an atherogenic role for phosphate exposure is demonstrated then phosphate binders could become the new statins.

Dairy Consumption, Blood Pressure, and Risk of Hypertension: An Evidence-Based Review of Recent Literature

Hypertension is a major risk factor for development of stroke, coronary heart disease, heart failure, and end-stage renal disease. In a systematic review of the evidence published from 2004 to 2009, the 2010 Dietary Guidelines Advisory Committee (DGAC) concluded there was moderate evidence of an inverse relationship between the intake of milk and milk products (dairy) and blood pressure. This review synthesizes results from studies published over the past year on the relationship between dairy intake, blood pressure, and hypertension risk. The influence of dairy micronutrients including calcium, vitamin D, potassium, and phosphorous on blood pressure and incident hypertension is examined. Emerging research on bioactive dairy peptides is also reviewed. Lastly, recent evidence on effects of dairy fat content on blood pressure and hypertension risk, and the impact of inclusion of low-fat dairy in dietary patterns is also investigated.

Donor phosphorus levels and recipient outcomes in living-donor kidney transplantation

BACKGROUND AND OBJECTIVES

In living-donor kidney transplantation, various donor factors, including gender, age, and baseline kidney function, predict allograft function and recipient outcomes after transplantation. Because higher phosphorus is predictive of vascular injury in healthy adults, the effect of donor phosphorus levels on recipient renal function after transplantation was investigated.

DESIGN, SETTING, PARTICIPANTS, AND MEASUREMENTS

Phosphorus levels in 241 living donors were analyzed from a 7-year period, and recipient renal function and acute rejection at 1 year posttransplantation were examined controlling for other influencing factors, including multiple donor variables, HLA matching, and acute rejection.

RESULTS

Female and African-American donors had significantly higher phosphorus levels predonation. By multivariable analysis, higher donor phosphorus correlated with higher recipient serum creatinine (slope=0.087, 95% confidence interval [CI]: 0.004 to 0.169, P=0.041) and lower recipient estimated GFR (slope=-4.321, 95% CI: -8.165 to -0.476, P=0.028) at 12 months. Higher donor phosphorus also displayed an independent correlation with biopsy-proven acute rejection and delayed or slow graft function after transplantation.

CONCLUSIONS

In a cohort of living kidney donors, higher donor phosphorus correlated with female gender and African-American ethnicity and was an independent risk factor for early allograft dysfunction after living-donor kidney transplantation.

Milk and dairy consumption and incidence of cardiovascular diseases and all-cause mortality: dose-response meta-analysis of prospective cohort studies

BACKGROUND

The consumption of dairy products may influence the risk of cardiovascular disease (CVD) and total mortality, but conflicting findings have been reported.

OBJECTIVE

The objective was to examine the associations of milk, total dairy products, and high- and low-fat dairy intakes with the risk of CVD [including coronary heart disease (CHD) and stroke] and total mortality.

DESIGN

PubMed, EMBASE, and SCOPUS were searched for articles published up to February 2010. Of > 5000 titles evaluated, 17 met the inclusion criteria, all of which were original prospective cohort studies. Random-effects meta-analyses were performed with summarized dose-response data. Milk as the main dairy product was pooled in these analyses.

RESULTS

In 17 prospective studies, there were 2283 CVD, 4391 CHD, 15,554 stroke, and 23,949 mortality cases. A modest inverse association was found between milk intake and risk of overall CVD [4 studies; relative risk (RR): 0.94 per 200 mL/d; 95% CI: 0.89, 0.99]. Milk intake was not associated with risk of CHD (6 studies; RR: 1.00; 95% CI: 0.96, 1.04), stroke (6 studies; RR: 0.87; 95% CI: 0.72, 1.05), or total mortality (8 studies; RR per 200 mL/d: 0.99; 95% CI: 0.95, 1.03). Limited studies of the association of total dairy products and of total high-fat and total low-fat dairy products (per 200 g/d) with CHD showed no significant associations.

CONCLUSION

This dose-response meta-analysis of prospective studies indicates that milk intake is not associated with total mortality but may be inversely associated with overall CVD risk; however, these findings are based on limited numbers.