Assessing How the Body Responds to Increased Phosphate Intake, and How This Response Depends on Age and Sex.

Forty subjects (males and females aged 18-25 or 63-70) will ingest an oral phosphate load, after which their body's response will be assessed by collecting blood and urine samples over a period of ten hours.

Inclusion criteria

• Healthy volunteers 18-25 and 63-70 years old
• 18.5 ≥ BMI < 26 kg/m2
• 0.84 ≥ phosphate in plasma ≤ 1.45 mM
• 2.20 ≥ calcium in plasma ≤ 2.50 mM
• 15 ≥ PTH in plasma ≤ 65 pg/ml
• eGFR ≥ 60 ml/min/1-73 m2
• 90 ≥ Systolic blood pressure ≤ 140 mmHg
• 60 ≥ Diastolic blood pressure ≤ 85 mmHg
• No hematuria and no acute urinary tract infection
• Ability and willingness to participate in the study
• Voluntary signed inform consent

Exclusion criteria

• Diabetes mellitus
• Pregnancy
• History of kidney stones
• History of parathyroidectomy
• History of anorexia nervosa
• History of bulimia
• History of solid organ transplantation.
• Nephrolithiasis
• Sarcoidosis
• Chronic pancreatitis
• Chronic diarrhea
• Chronic liver disease
• Complete distal renal acidosis (dRTA)
• Cystinuria
• Hypo- or hyperaldosteronism
• Hyper- or hypotension
• Hypernatremia
• Gastrointestinal disorders
• Known hypersensitivity reactions to azoic dyes, acetylsalicylic acid, as well as antirheumatic drugs and painkillers (prostaglandin synthesis inhibitors).

Intake of vitamin D and calcium supplements, phosphate, bisphosphonates, cinacalcet, denusomab, teriparatide, systemic glucocorticoids or mineralcorticoids, antiepileptics, carboanydrase inhibitors or diuretics