What kidneys do
They filter around 180 litres of blood a day, balance sodium, potassium and fluid, control blood pressure, activate vitamin D and signal the marrow to make red blood cells.
How damage starts
High glucose and high pressure damage the tiny filtering units. The first measurable sign is usually albumin leaking into urine, long before creatinine or eGFR shift. Ask about a urine albumin test if you have diabetes or hypertension.
Everyday protection
Keep blood pressure and glucose in range, stay hydrated, keep sodium moderate, avoid routine high-dose NSAIDs, and be cautious with very high protein loads if kidney function is already reduced.