Nocturnal eating disturbs phosphorus excretion in young subjects: a randomized crossover trial

Diurnal variation of serum phosphorus concentrations in intact male adult domestic cats

BACKGROUND

Monitoring serum phosphorus concentrations is crucial in the management of chronic kidney disease in cats. The diurnal variation of serum phosphorus concentration may affect clinical assessment.

HYPOTHESIS/OBJECTIVES

Characterize the diurnal variation of serum phosphorus concentration in cats and determine the associations between changes in serum phosphorus concentration and several metabolites of phosphorus metabolism.

ANIMALS

Six apparently healthy, intact male, specific-pathogen-free cats were housed in a photoperiod, humidity, and temperature-controlled facility.

METHODS

Blood sampling was performed hourly for 24 hours to obtain the serum concentrations of phosphorus, ionized calcium, parathyroid hormone, and calcidiol. Results were analyzed using linear mixed-effect models to determine the significance of diurnal variation and associations between serum phosphorus concentrations and other metabolites over time.

RESULTS

Diurnal variation in serum phosphorus concentration was noted with an apex around 11:00 followed by gradually declining concentrations to reach the nadir around 23:00. The serum phosphorus concentration again increased through the early morning on the next day. An approximately 25% difference in serum phosphorus concentration at the apex and the nadir was documented. A non-linear relationship between the serum concentrations of phosphorus and ionized calcium over time was identified.

CONCLUSIONS AND CLINICAL IMPORTANCE

Diurnal variations of serum phosphorus concentration and associations between the trending of serum phosphorus and ionized calcium concentrations were evident in a group of clinically healthy adult cats housed in a controlled environment. These findings can help in the interpretation of clinical and research data regarding calcium and phosphorus metabolism and kidney health in cats.

Diurnal rhythms of urine volume and electrolyte excretion in healthy young men under differing intensities of daytime light exposure

In humans, most renal functions, including urine volume and electrolyte excretions, have a circadian rhythm. Light is a strong circadian entrainment factor and daytime-light exposure is known to affect the circadian rhythm of rectal temperature (RT). The effects of daytime-light exposure on the diurnal rhythm of urinary excretion have yet to be clarified. The aim of this study was to clarify whether and how daytime exposure to bright-light affects urinary excretions. Twenty-one healthy men (21–27 years old) participated in a 4-day study involving daytime (08:00–18:00 h) exposure to two light conditions, Dim (< 50 lx) and Bright (~ 2500 lx), in a random order. During the experiment, RT was measured continuously. Urine samples were collected every 3 ~ 4 h. Compared to the Dim condition, under the Bright condition, the RT nadir time was 45 min earlier (p = 0.017) and sodium (Na), chloride (Cl), and uric acid (UA) excretion and urine volumes were greater (all p < 0.001), from 11:00 h to 13:00 h without a difference in total daily urine volume. The present results suggest that daytime bright light exposure can induce a phase shift advance in urine volume and urinary Na, Cl, and UA excretion rhythms.

Associations of food groups and cardiometabolic and inflammatory biomarkers: does the meal matter?

Increased attention has been paid to circadian patterns and how predisposition to metabolic disorders can be affected by meal timing. Currently, it is not clear which role can be attributed to the foods selected at meals. On a cross-sectional sub-cohort study (815 adults) within the European Prospective Investigation into Cancer and Nutrition-Potsdam study, we investigated whether the same foods (vegetables, fruits, refined grains, whole grains, red and processed meats) eaten at different meals (breakfast, lunch or dinner) show different associations with biomarkers of cardiometabolic risk. Meal-specific usual intakes were calculated from multiple 24-h dietary recalls. Multivariable-adjusted linear regression models showed that intake of vegetables at breakfast was associated with lower LDL-cholesterol (-0·37 mmol/l per 50 g; 95 % CI -0·61, -0·12) and vegetables at dinner was associated with higher HDL-cholesterol (0·05 mmol/l per 50 g; 95 % CI 0, 0·10). Fruit intake at breakfast was associated with lower glycated Hb (HbA1c) (-0·06 % per 50 g; 95 % CI -0·10, -0·01) and fruits at dinner with lower C-reactive protein (CRP) (-0·21 mg/l per 50 g; 95 % CI -0·42, -0·01). Red and processed meat intake at breakfast was associated with higher HbA1c (0·25 % per 50 g; 95 % CI 0·05, 0·46) and CRP (0·76 mg/l per 50 g; 95 % CI 0·15, 1·36). Our results suggest that by preferring fruits and vegetables and avoiding red and processed meats at specific meals (i.e. breakfast and dinner), cardiometabolic profiles and ultimately chronic disease risk could be improved. Lunch seemed to be a less important meal in terms of food-biomarker associations.

Soymilk intake has desirable effects on phosphorus and calcium metabolism

The objective was to evaluate the effect of replacing milk with soymilk or calcium-fortified soymilk as a part of a meal on postprandial serum phosphorus levels. This study had a randomized crossover design. Ten healthy subjects were enrolled and consumed three test meals that contained either milk, soymilk, or calcium-fortified soymilk containing the same amount of calcium as milk. Blood samples were collected at 0, 30, 60, 120, 240 and 360 min and urine samples were collected from 0 to 360 min after consuming the test meal. Serum phosphorus levels decreased the most after the ingestion of the soymilk meal, and the least after the ingestion of the milk meal. After the ingestion of each meal, serum intact parathyroid hormone levels showed an initial drop followed by a gradual rise, and these changes were more pronounced for the soymilk meal than for the milk meal and the soymilk + calcium meal. Our study shows that replacing milk with soymilk as a part of a meal may suppress the postprandial elevation in serum phosphorus levels, even when the soymilk contains the same amount of calcium as milk.