Does high blood pressure cause heart disease? Or does something else cause both? Shouldn’t we be using the best methods that science can offer to answer this question?
Com
ment on “Nearly 1 In 5 Young Adults Have High Blood Pressure” on Morning Edition on 26 May 2011. This is a report on some of the results of a 13 year survey of adolescent lifestyles, attitudes, nutrition, and health outcomes. I caution the reader against reaching the same conclusions as the researchers did about high blood pressure being caused by obesity. No one has tested the possibility that something else might be causing both, since both conditions involve a breakdown or foul-up in cellular metabolism.
Updated: 2 Sept 2014
Summary:
NPR reporter Patti Neighmond interviewed sociologist Kathleen Mullan Harris at the University of North Carolina, one of several researchers (Nguyen et al., 2011) who found that the prevalence of hypertension (>140/90 mm Hg blood pressure) was greater than previously thought–one out of five 24-to-32-yr-olds (most recent data was from 2008). This report was one of many reports using data gathered on 14,000 teenagers, starting in 1995, as part of a larger study on health and social aspects of life in the National Longitudinal Study of Adolescent Health (Add Health, NIH). The findings in this study are serious because high blood pressure eventually can make the body more vulnerable to ruptured blood vessels, blood clots, internal bleeding, diabetes and heart disease (Dr. Steven Hirschfeld, NIH). In 1995 only 11% of 12-19-yr-olds were obese. On follow-up five years later (study population =17-24), 22% were obese. By 2008, 67% of all young adults (which reflects national trends for all young adults) were overweight or obese. Patti Neighmond says that obesity “is known to cause high blood pressure”. However, a note of caution–other federal studies show less than one out of five young adults had hypertension, so more study is needed. Dr. Hirschfeld says that everyone should have checkups where their weight, blood pressure, and blood sugar and other measurements are made. However, a typical 20-something won’t get regular checkups or check their blood pressure.
My Comments at NPR
Researchers need to be careful about implying a cause for the high blood pressure. Just because high blood pressure seems to go with obesity doesn’t mean it results from the obesity. No controlled experiment has been done where a group of adolescents have been made obese, using particular methods that all can agree can cause obesity (e.g. overeating and lack of exercise), checking blood pressure all through the study, and found that high blood pressure does not appear until the adolescents reach obese weight, and then having these adolescents lose the excess weight and found that the high blood pressure has come back down to normal. Adequate controls must include environmental variables (like exposure to toxins and psychological factors), usually not included in any study. Correlation does not give Causation. This caution should be exercised so that researchers actually look for a cause instead of assuming one.
Note of Caution: Patti Neighmond says that steps could be done to make it easier for people to check on their blood pressure for free, like putting stations in pharmacies, airports, shopping malls etc. The CBS TV show The Doctors (www.TheDoctorsTV.com) discussed a report done last year that showed most of these stations are in fact inaccurate and need to be calibrated often. The pharmacies have stepped up to this and most now regularly calibrate them, but you cannot say that the other businesses have done so. A person needs to ask someone at the store if they can give a date when the machine was last calibrated. If they cannot, it is probably not reliable. Researchers have found that the blood pressure readings done at the doctors’ offices tend to be inaccurate also because the patient is usually under some stress at the time. The best readings have come from patients who own a blood pressure cuff and take their own blood pressure readings at home, when inactive and relaxed.
Problem With This Report: Cause and Effect
History is important here. The report says that Federal health officials claim that the expanding waistlines and higher BMI of young adults are CAUSING unexpected problems: increase in diabetes, kidney disease and even arthritis. Which came first, the higher BMI, the hypertension or any of these disorders? The study was based upon surveys of teenage health starting in 1995, called the National Longitudinal Study of Adolescent Health, funded by NIH, with 14,000 participants. It doesn’t matter that the study included a very large database. No experiment was done to show cause and effect. So none of this study’s results can show that being overweight or obese CAUSES hypertension. There is also a distinct possibility that the hypertension existed before the obesity rate, simply because, as the study says, young adults are less likely to visit a doctor or routinely have their blood pressure checked. Hypertension, or any of these problems existing BEFORE obesity occurs tells researchers that they need to examine something else that might actually be causing all of these problems–e.g. environmental toxins. See my discussion of Cholesterol and Heart Disease.
I wish NPR would post on their rundowns the sources they used for their reports, so listeners can go to the originals. Even the ones requiring a subscription can be gotten at many university libraries for free.
References
Häggström, M. (2014). Medical gallery of Mikael Häggström 2014. Wikiversity Journal of Medicine, 1 (2). DOI:10.15347/wjm/2014.008. ISSN 20018762.
Nguyen, Q. C., Tabor, J. W., Entzel, P. P., Lau, Y., Suchindran, C., Hussey, J. M. … Whitsel, E. A. (2011). Discordance in national estimates of hypertension among young adults. Epidemiology, 22(4), 532-541. [Freely Available at NCBI].
The data (National Longitudinal Study of Adolescent Health, one of several websites), is supposed to be available for public viewing, but you need to be associated with a research institution who is a member of the ICPSR to get access to some of the data. If not, you must pay $500 per data set.
For other reports on nutrition, see Nutrition Reviews
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© Copyright 2014 by Martha L. Hyde and https://marthalhyde.wordpress.com.
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