Straight Lines Rarely Describe Nutrition and Health Outcomes
Are you a supporter of banning, restricting, or limiting certain food substances? Maybe sugar? Or some fats? Or salt? If so, you should read this interesting paper published in JAMA on J-shaped associations. Chokshi and colleagues use alcohol consumption as an example. However, most nutrient exposure/mortality relationships are J-shaped. Policies based on linear relationships and simplistic calls to limit, restrict, or ban nutrients or food components are naive and can be misleading.
It is easy to assume black and white positions on compounds where a linear relationship between exposure and health outcome exists, i.e. tobacco. Another example would be methylene chloride often used to strip bathtubs. In both cases, a linear relationship exists between exposure and mortality.
The Body Mass Index (BMI) and mortality risk is curvilinear. A more recent systematic review with >650,000 individuals found U- or J-shaped associations of BMI and Waist Circumference (WC) with mortality.
Many nutrition/food component and health relationships are not linear. Although trans-fatty acids (TFA) are associated with cardiovascular mortality, the risk seen with dietary intake is curvilinear. As intakes rise from 1.3 to 2.0 g TFA per day mortality risk decreases and then increases dramatically as TFA intake average 8.2 g TFA daily.
Vitamin E is another example. The relationship between serum α-tocopherol concentrations and mortality is a reverse J-shape with the greatest change in mortality risk observed in people with serum α-tocopherol concentrations <30 µmol/L. Indeed, 2/3 of Americans fail to meet the criterion of vitamin E adequacy associated with vitamin E RDA.
In the field of nutrition, J-shaped curves are commonplace. Without “precise mapping of the inflections of epidemiologically important J-shaped relationships as well as understanding how many people are actually distributed along different points on the curve”, it isn’t possible to formulate sound policy or provide proper guidance to consumers.
Readers, we have a call for action!
Chokshi DA, El-Sayed AM, Stine NW. J-shaped curves and public health. 2015 JAMA doi: 10.1001/jama.2015.9566
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Adachi H. Trans fatty acid and coronary artery disease – Lessons from seven countries study. Circulation J doi: 10.1253/circj.CJ-15-0743
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Wright ME, Lawson KA, Weinstein SJ, Pietinen P, Taylor PR, Virtamo J, Albanes D. Higher baseline serum concentrations of vitamin E are associated with lower total and cause-specific mortality in the Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study. 2006. AJCN 84(5):1200-1207
McBurney MI, Yu EA, Ciappio ED, Bird JK, Eggersdorfer M, Mehta S. Suboptimal serum α-tocopherol concentrations observed among younger adults and those depending exclusively upon food sources. 2015 PLOS ONE doi: 10.1371/journal.pone.0135510