Two child specialists issue a timely reminder in the December 22 issue of the British Medical Journal . Indianpolis-based Rachel C Vreeman, a fellow in children's health services research, and Aaron E Carroll, an assistant professor of pediatrics, remind physicians not to be taken in by myths perpetuated in medical science:
Physicians understand that practicing good medicine requires the constant acquisition of new knowledge, though they often assume their existing medical beliefs do not need re-examination. ...
Even physicians sometimes believe medical myths contradicted by scientific evidence.
The prevalence and endorsement of simple medical myths point to the need to continue to question what other falsehoods physicians endorse.
Examining why we believe myths and using evidence to dispel false beliefs can move us closer to evidence based practice.
Let's face it, doctors are busy people. Reading all the latest journals -- and, particularly, the methods sections that often contain the key statistical manipulations -- is a virtually insurmountable task for GPs or area specialists like those serving our children. Take, for example, an aricle on salt and blood pressure in children published in the Journal of Human Hypertension in September 2007 by anti-salt war chief Graham MacGregor and his associates. MacGregor et al reported that
An increase of 1g/day in salt intake was related to an increase of 0.4 mm Hg in systolic and 0.6 mm Hg in pulse pressure....The consistent finding of our present analysis of a random sample of free-living indiviudals with that from controlled salt reduction trials provides further support for a reduction in salt intake in children and adolescents.
That's the item that may have caught readers' attention and, if so, it would have perpetuated another myth -- that salt was important to the blood pressure of children. Don't blame the journal, however; the editors commissioned an editorial to attempt to keep the story straight -- and they continue to make that editorial available as their top-listed Featured Article. In that corrective editorial , fomer International Society of Hypertension president Michael H. Alderman explains:
Specifically, a difference in salt intake of 1 g was associated with a 0.4 mm Hg rise in blood pressure. However, the significance of this relationship disappeared after correction for energy intake. ...
Regrettably, the current report provides little information regarding other associations to blood pressure or variations in other characteristics that might be associated with variations in sodium intake. For example, stature and physical maturation are associated with blood pressure. Bigger children may be muscular or pudgy. Children who exercise vigorously may have large energy (and sodium) intakes, and be taller and leaner than youngsters who have the same body mass index and different life styles. Cooper et al. postulated that the strong link of creatinine to blood pressure might reflect muscle mass and perhaps be a marker of body size. This, in turn, might be the most powerful determinant of blood pressure in children-more important than age or sodium. Perhaps, the best measure of growth and development available here is mid-arm circumference. The strong arm to blood pressure correlation may reflect muscle mass and suggests that diets high in energy (and therefore, among other things, sodium) may be conducive to physical maturation, along with a slightly higher blood pressure. In short, if this were the causal pathway, then higher pressure might even be a desirable sign in children.
Dietary intake is complex, and to characterize it on the basis of one element may well oversimplify any assessment of its value. For example, given the high correlation of energy with virtually all other nutrients, it is possible that those consuming more sodium (and energy) had more satisfactory consumption of other important dietary elements-both known and unknown. In any event, blood pressure is not the only measure of the health of children. The British Survey of Young People probably includes, in addition to physical and physiological data, information on other social, economic and developmental characteristics whose explanation might well inform our understanding of the relation of blood pressure, diet, health and development in these youngsters. Of note, He et al. also provide some other interesting information. For example, they note that 18-year-old British residents, in 1997, were consuming 2.6-g of sodium per day. That was similar to levels found in Chicago a decade earlier, and falls within the range of adult sodium intake seen world-wide in most countries and suggests that, a decade and 2 ago, these near adults were within that range.
It is also interesting to note that measures of discretionary sodium use did not correlate with blood pressure. This supports the Cochrane Collaboration conclusion that there was not sufficient evidence for a general dietary recommendation to reduce sodium intake. (emphasis added)
Medical myths can cause real damage. With regard to children, it seems that once corrected for caloric intake, there is no association of blood pressure and salt intake, but there IS a strong association of calories (and salt) with healthy development of children. Perhaps the biggest myth is that diet is less important than its component nutrients. Don't let your pediatrician get duped or pass on medical mythology.
