Sodium is the leading dietary factor associated with urinary calcium excretion in Hong Kong Chinese adults

We conducted a cross-sectional population-based study comprising 1010 Hong Kong Chinese (500 men and 510 women) aged 25-74 years during 1995-6. The st udy examined the important dietary, lifestyle and anthropometric factors as sociated with urinary calcium excretion. Dietary intakes were assessed by m eans of food frequency questionnaire. Spot urine was collected to measure t he urinary excretion profiles of calcium (Ca), sodium (Na), potassium (K) a nd creatinine (Cr). When expressed as ratios of cations to urinary Cr, sign ificant relationships were noted between urinary Ca and Na (r: similar to 0 .6), and between urinary Ca and K (r: 0.17-0.21). Stepwise multiple linear regression analyses were carried out separately in men and women aged below and above 50 years. We found that urinary Na/Cr was the leading independen t factor associated with urinary Ca/Cr in all four age and sex groups. It a ccounted for 22% of urinary Ca/Cr variations in women aged below 50 years, and 35-43% in the other three age and sex groups. We estimated that urinary Ca excretion increased by about 1.4 (range 1.37-1.43) mmol per 100 mmol in crease in urinary Na. Except in men aged 50 years and over, urinary K/Cr wa s inversely associated with urinary Ca/Cr in all groups. Age was independen tly and positively associated with urinary Ca/Cr in subjects aged below 50 years. We did not observe any significant relation between urinary Ca/Cr an d dietary protein, phosphorus, alcohol drinking and smoking. In conclusion, we found that urinary Na/Cr, but not dietary protein., Ca or phosphorus, i s the most important factor influencing urinary Ca/Cr excretion in our popu lation. Urinary K is a potential factor for Ca conservation.