A federally promoted diet to control hypertension may also lower the risk of kidney stones, a new study suggests.

The Dietary Approaches to Stop Hypertension (DASH) diet—which is encouraged by the National Heart, Lung, and Blood Institute—advises low sodium intake and consumption of fruits, vegetables, whole grains, low- and nonfat dairy products, fish, and poultry, and discourages consumption of red meat and sugar.

A team led by Eric N. Taylor, MD, of the Channing Laboratory in Boston, examined the effect of a DASH-style diet on stone risk in three large prospective studies: the Health Professionals Follow-up Study (HPFS), which included 45,821 men aged 40 to 75 years and had 18 years of follow-up; the Nurses’ Health Study I (NHS I), which included 94,108 women aged 30-55 years at enrollment and had 18 years of follow-up; and the Nurses’ Health Study II (NHS II), which included 101,837 women aged 25-42 at enrollment and had 14 years of follow-up.

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The investigators constructed a DASH score based on high intake of fruits, vegetables, nuts and legumes, low-fat dairy products, and whole grains, and low intake of sodium, sweetened beverages, and red and processed meats.

A total of 5,645 kidney stones occurred during a combined 50 years of follow-up. Subjects with higher DASH scores had higher intakes of calcium, potassium, magnesium, oxalate, and vitamin C and lower intakes of sodium.

Compared with HPFS subjects in the lowest quintile of DASH score, those in the highest quintile had a 45% reduced risk of kidney stones after adjusting for age, BMI, fluid intake, hypertension, diabetes and other potential confounders, according to a report in the Journal of the American Society of Nephrology (2009;20:2253-2259). Among subjects in NHS I (older women) and NHS II (younger women), those in the highest quintile had a 42% and 40% reduced risk of kidney stones compared with the lowest quintile.

The consistent association between consumption of a DASH-style diet and a reduced risk of kidney stones in all three cohorts “is remarkable” in light of previous studies showing substantial differences in individual dietary factors and stone risk between men, older women, and younger women.

The researchers cited previous studies demonstrating that animal protein intake was associated with a higher risk of kidney stones in men but not women, and potassium intake was strongly associated with a reduced stone risk in men and older women, but not younger women.

Although most of the stones that occurred in the study populations were likely calcium oxalate stones, Dr.  Taylor and his colleagues noted, a DASH-style diet could also decrease the risk of other stone types. “By decreasing uric acid production and increasing urinary pH, reducing consumption of animal flesh may decrease the risk of uric acid stones,” they stated. “Higher intake of fruits and vegetables also may raise urine pH and reduce the risk of uric acid crystal formation.”

The higher oxalate content of the DASH-style diet—the result of increased intake of fruits, vegetables, and nuts—may increase urinary oxalate, a major risk factor for calcium oxalate stone formation. Consumption of fruits and vegetables, however, also raises urinary citrate, an important inhibitor of calcium stones, the investigators explained. In addition, the higher calcium content of the DASH-style diet may minimize any adverse effect of higher oxalate intake.

“Although we think it reasonable for calcium oxalate stone formers with high levels of urinary oxalate to avoid intake of some individual foods very high in oxalate (such as spinach and almonds), our data do not support the common practice of dietary oxalate restriction in calcium stone formers, particularly if such advice results in lower intake of fruits, vegetables, and whole grains,” they wrote.