Writing in the American Heart Association journal Hypertension, two research teams, one in the Netherlands and the other in the United States, report that dietary levels of these and other nutrients during formative months and years appear to be "important determinants" of blood pressure.
In the Dutch study, researchers re-tested blood pressures of 167 children who, as infants, had been in a 1980 trial of sodium-lowering on blood pressure during the first six months of their lives 15 years earlier. Youngsters who had been on a low-sodium diet and had lower blood pressures at the end of that six-month trial still had lower pressures when re-examined 15 years later, compared with those who as infants ate "normal" amounts of sodium.
In the U.S. study, an analysis of nutrient intake among adolescents found that children who consumed more calcium and fiber had lower diastolic blood pressure, while eating more dietary fat was linked to higher diastolic pressure. Diastolic blood pressure, the "lower" number in a blood pressure reading, measures pressure between heartbeats.
The Dutch study, conducted by scientists at Rotterdam's Erasmus University Medical School, found that the children who had been in the original low-sodium diet group had diastolic blood pressures that were 2.2 millimeters of mercury (mm Hg) lower than the normal-sodium group. These children also had systolic blood pressures (the "upper" number, reflecting pressure as the heart contracts) that were 3.6 mm Hg lower than the normal-sodium group.
Small changes in blood pressure could prove significant over the course of a lifetime.
The "low-sodium" diet in the 1980 trial contained 120 milligrams (mg) of sodium per day (corresponding to 300 mg of table salt) while the "normal" diet contained 330 mg of sodium (corresponding to 821 mg of table salt). The American Heart Association recommends a diet that includes no more than 2.4 grams of sodium, equal to about one-and-a-quarter teaspoons of table salt, per day.
The Dutch team speculates that "environmental exposures," which includes diet, occurring very early in life -- when "programming" of the body's organs and systems take place -- may be more important to the development of heart disease and stroke than similar exposures in adulthood.
Hypertension expert Theodore Kotchen, M.D., says the study shows that "differences in salt intake in infancy may have a long-term effect on blood pressure." But Kotchen, chairman of medicine at the Medical College of Wisconsin, Milwaukee, cautions, "While the research suggests it's beneficial to avoid a high-salt diet for infants, inadequate intake of salt, which could have serious adverse consequences for the health of the child, and rigorous salt restriction, are not advisable."
In the second study reported today in Hypertension, investigators conducting the Dietary Intervention Study in Children (DISC) also studied the relationships between nutrients and blood pressure in boys and girls from ages 8-11 to ages 11-14. All of the children had high levels of "bad" LDL (low-density lipoprotein) cholesterol, which leads to the formation of blood vessel narrowings that can result in heart attacks and strokes. The children had been part of a dietary intervention study to learn whether lowering fat intake would reduce their LDL levels, which averaged 130 milligrams per deciliter (mg/dl) of blood.
The scientists gathered dietary information from 662 children over three years and recorded the children's blood pressures. Nutrients studied included calcium, magnesium and potassium -- so-called "micro-nutrients" that have important functions in the body. Also analyzed were calorie-containing nutrients, such as protein; carbohydrates and fat, as well as those that do not have calories -- cholesterol and fiber. Information on salt intake was not included. Adjustments were made for height, weight, sex and total calories consumed.
"When we examined each nutrient by itself, eating more calcium, magnesium, potassium, protein or fiber was associated with lower blood pressure, and eating more total fat was associated with higher blood pressure," reports lead investigator Denise G. Simons-Morton, M.D., Ph.D., of the National Heart, Lung, and Blood Institute in Bethesda, Md. When the researchers looked at all nutrients together, she says, only consuming more calcium and fiber was associated with lower diastolic pressure, while eating more fat was associated with higher diastolic pressure. Higher systolic blood pressure was related only to increased total dietary fat, the authors add.
The blood pressure differences observed, while significant, were still small, the scientists concede. A 2.5-mm-Hg drop in diastolic blood pressure came only after eating 330 milligrams more of calcium and 4 additional grams of fiber per day while also reducing daily fat intake by 19 grams. But even small reductions in blood pressure can be important, Simons-Morton says, "when magnified throughout large populations and in individuals over the course of a lifetime."
A "downward shift" of 2 mm Hg systolic blood pressure in the adult population "would save an estimated 12,000 lives per year in the United States," the study's authors point out. And they cite a major study showing that lowering diastolic blood pressure by only 4 mm Hg "caused a marked reduction in all-cause mortality in adults."
Simons-Morton noted that earlier studies of nutrients' effects on blood pressure in children and adolescents have been "inconsistent and inclusive." Because the analysis of blood pressure was not the main purpose of DISC, she describes the new results as "exploratory" and deserving of further study. One finding -- that eating more monounsaturated fat (the kind of fat found in olive oil) was associated with higher diastolic blood pressure -- was particularly surprising and in need of verification, she says.
Because the study included only children with high "bad" cholesterol, the researchers say their findings aren't automatically applicable to all children. They say additional research "should help refine" current recommendations for primary prevention of high blood pressure. These include lowering weight, reducing sodium and alcohol, increasing potassium intake and increasing aerobic physical activity. Of primary importance in attaining these goals, the authors add, is "identifying determinants of blood pressure in children."
Authors of the Dutch study were: Johanna M. Geleijnse, Ph.D.; Albert Hofman, M.D.; Jacqueline C.M. Witteman, Ph.D.; Alice A.J.M. Hazebroek, M.D.; Hans A. Valkenburg, M.D.; and Diederick E. Grobbee, M.D.
Simons-Morton's co-investigators were: Sally A. Hunsberger, Ph.D.; Linda Van Horn, Ph.D., a member of the American Heart Association's Nutrition Committee; Bruce A. Barton, Ph.D.; Alan M. Robson, M.D.; Robert P. McMahon, Ph.D.; Linda E. Muhonen, M.D.; Peter O. Kwiterovich, M.D., Ph.D.; Normal L. Lasser, M.D., Ph.D.; Sue Y.S. Kimm, M.D.; and Merwyn R. Greenlick, Ph.D.
Participating institutions in the NHLBI-sponsored study include Northwestern University Medical School, Chicago; Maryland Medical Research Institute and Johns Hopkins University, both in Baltimore; Children's Hospital, New Orleans; University of Iowa, Iowa City; New Jersey Medical School, Newark; University of Pittsburgh; and Kaiser Permanente Center for Health Research, Portland, Ore.
Hypertension is one of five scientific journals published by the Dallas-based American Heart Association.
Media advisory: Dr. Geleijnse's phone number in Rotterdam is 31 10 408-8228; fax 436-5933; Dr. Simon-Morton's phone number is (301) 435-0384; fax 480-1669. Reporters may call (214) 706-1173 for copies of their journal reports. (Please do not publish phone or fax numbers.)