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Source: Lin PH, et al. The DASH diet and sodium reduction improve markers of bone turnover and calcium metabolism in adults. J Nutr 2003;133:3130-3136.
Osteoporosis is a preventable disease that increases the risk of fracture for more than 10 million American men and women, causing more than 1.5 million fractures per year.1 These fractures result in significant morbidity and mortality for populations at risk and represent a large cost (estimated at $14 billion per year) for an already strained health care system.1 Projections suggest that these numbers only will increase as our baby boomer population ages. An additional 34 million Americans have osteopenia now, and dramatic increases in osteoporosis are anticipated by 2050 due to aging and the cumulative effects of poor diet and lifestyle habits.1 Current therapy focuses on calcium and vitamin D replacement, along with more aggressive pharmaceutical measures, such as bisphosphonates. Risk factor modification, especially if started early in life, can allow formation of maximum bone mass and reduce the age-related decline in bone density. Increasing weight-bearing exercise, stopping smoking, and decreasing alcohol and caffeine intake commonly are recommended. However, recent literature suggests that dietary modifications, beyond increased calcium intake, may be helpful in maintaining healthy bone mass. Some of these factors may not be immediately obvious to patients or practitioners.
Over the last decade, a number of significant observations have been made regarding diet and bone health. First, there are data suggesting that the acid-base balance of the body may affect the rate of absorption of calcium from bone, as it has been observed that increased acidity increases the rate of calcium loss in the urine. In effect, the large mass of bone acts as a buffer to maintain the acid-base balance of the body. Certain foods, such as meat, grains, and some cheeses, and metabolic states, such as starvation or diabetic ketoacidosis, are felt to increase the acidity of the body. Other dietary constituents besides calcium also have been noted to affect bone density. For example, positive benefits on bone metabolism have been noticed in observational studies of subjects eating a diet high in fruits and vegetables. Increasing fruit and vegetable consumption from 3.6 to 9.5 servings per day decreased urinary calcium excretion by one-third.2 In addition, high dietary sodium loads have been associated with an increase in urinary calcium loss, especially in postmenopausal women.3 Even small losses of calcium can have profound effects over a time. It has been calculated that the net loss of 1 mmol/d of calcium could lead to the loss of one-third of the bone mass of a normal adult over two decades, if no other compensatory mechanisms intervened.4 Thus, even small changes related to dietary interventions could prove very significant in the prevention or modification of osteoporosis.
Lin and colleagues tested the effects of a diet rich in fruits, vegetables, and low-fat dairy products (Dietary Approaches to Stop Hypertension [DASH] diet) in a randomized clinical trial designed to test the diet’s effect on blood pressure.5 Two of the trial sites involved in the larger trial also included measurements designed to examine the effect of the dietary intervention on bone health. The DASH diet differs from the standard American diet in that it is lower in acid load, fats, and cholesterol; is higher in potassium, calcium, and magnesium; and derives more phytochemicals from fruits and vegetables. The trial also included three daily sodium levels: higher (3.5 g), intermediate (2.3 g), or lower (1.1 g). Subjects were adults with mild or borderline elevations in systolic and/or diastolic blood pressure defined as blood pressure greater than 120/80. The group was a little over half women, mainly Hispanic and African-American, who had an average BMI of 29, suggesting that they were overweight, bordering on obese. Subjects were randomly assigned to either the DASH diet or a conventional Western diet for three 30-day trials at each of the three sodium levels. Subjects were given all of their food and the caloric content was adjusted to maintain their starting weight.
Outcomes included serum measures of bone formation (OC) and resorption (CTX), urinary calcium (UC), and parathyroid hormone (PTH) levels. The DASH diet decreased OC by 11-18% and CTX by 16-18%. Both of these markers of bone resorption were significantly reduced at all three sodium levels. No change was noted in the levels of PTH or UC comparing the DASH diet overall to control. The effect of sodium was more mixed on markers of bone reformation and PTH. However, urine calcium concentrations decreased in a dose- dependent manner with decreasing sodium intake in both control and DASH diet participants. Thus, the DASH diet showed a benefit in reducing the markers of bone turnover. In addition, lowering sodium led to a decrease in urinary calcium loss, another potentially negative factor for bone mass.
Despite the fact that the exact mechanism by which the DASH diet positively affects bone health is unknown, health professionals should be vigorously recommending this style of diet to patients. Besides the bone benefits, additional favorable outcomes for cardiovascular health have been seen with lower blood pressure (both systolic and diastolic in patients with mildly elevated blood pressure), as well as reduced serum homocysteine, total cholesterol, and LDL. There appears to be little downside to this diet and we should make every effort to encourage our patients (and ourselves!) to comply with it.
Information and a patient education handout about this diet are available at the National Heart Lung and Blood Institute’s web site.6 Materials include patient handouts, recipes, and diet diary forms, making it easy for you to educate your patients about this heart- and bone-healthy diet. This diet gives a whole to meaning to the adage: Eat well and be strong.
Dr. Hardy, Associate Director, UCLA Center for Dietary Supplement Research: Botanicals Medical Director, Cedars-Sinai Integrative Medicine Program Los Angeles CA, is on the Editorial Advisory Board of Alternative Therapies in Women’s Health.