Experimental evidence suggests an association between hypertension and abnormalities of calcium metabolism that could lead to increased calcium loss, secondary parathyroid hyperactivity and loss of calcium from bone. Because this association could have serious consequences in elderly women already at risk for osteoporosis, Cappuccio and colleagues studied bone density in women in a longitudinal health study that began in 1988.

The prospective health study included more than 9,000 white women older than 65 years of age who were able to walk unaided and had no history of hip replacement. The present study included 3,676 women who had bone densitometry of the proximal femur measured at baseline and again 3.5 years later, and who were not taking thiazide diuretics at the time of assessment. Data gathered on these women included weight, height, medication history (especially current hormone replacement therapy, antihypertensive agents and diuretics) and smoking history. Blood pressure and pulse were measured under controlled and standardized conditions at each visit.

The average age of the women was 73 years, and they were generally healthy. Only 7.9 percent smoked, and 15.5 percent took hormone replacement therapy. After an average follow-up of 3.5 years, the mean yearly loss of femoral-neck bone density was 3 mg per cm² (0.5 percent). Nearly 17 percent of the women were regularly taking antihypertensive therapy. Women who smoked experienced greater bone loss; women taking hormone replacement therapy showed a slower rate of loss. Absolute and relative bone loss was also significantly associated with age. After adjustment for weight change, initial bone density, smoking, age and hormone replacement therapy, the rate of bone loss was significantly associated with systolic blood pressure. The annual rate of bone loss (yearly absolute changes) in women in the lowest systolic blood pressure quartile was −2.26 mg per cm² compared with −3.79 mg per cm² in women in the highest quartile. An association with diastolic blood pressure was found in women who were younger than 75 years of age.

The authors found a significant interaction with age in the relation between diastolic blood pressure and bone mineral loss, which they propose results from abnormalities in calcium metabolism, including secondary hyperparathyroidism and increased urinary calcium excretion for a given sodium intake. Because osteoporosis is a significant public health problem, they advocate greater use of thiazide diuretics and reduction of sodium intake to counteract the vulnerability to osteoporosis in elderly white women—particularly those with hypertension.