Oral glucose tolerance test results may be influenced by height, study finds

Among both men and women in Finland, height was inversely associated with two-hour plasma glucose concentration, except among patients with a body-mass index of 35 kg/m2 or more.

Up to a certain category of body mass index (BMI), taller people may have lower two-hour plasma glucose concentrations during oral glucose tolerance testing than shorter people, a recent study found.

To examine the relationship between height and glucose regulation, researchers used 2005 to 2007 data from a population survey conducted in Finland. Their analysis included 2,659 participants ages 45 to 70 years who were without serious comorbidities but at elevated risk of developing cardiovascular disease or type 2 diabetes.

All participants underwent an oral glucose tolerance test and had their height and BMI recorded. Participants were divided into five height-level categories based on normal distribution (12.5%, 25%, 25%, 25%, and 12.5% of the total distribution) and, in further analyses, were divided into four BMI groups (<25 kg/m2, 25 to 29.9 kg/m2, 30 to 34.9 kg/m2, and ≥35 kg/m2). Results were published online on May 29 by Diabetic Medicine.

Among both men and women, height was inversely associated with two-hour plasma glucose concentration (but not with fasting plasma glucose concentration) in an age-adjusted analysis. There were no significant differences between genders, both of which had lower mean two-hour plasma glucose concentrations as height increased.

When researchers factored BMI into their calculations, they found that the inverse relationship between height and two-hour plasma glucose concentration persisted in the three lowest BMI groups (P<0.001 for <25 kg/m2; P=0.001 for 25 to 29.9 kg/m2; and P=0.015 for 30 to 34.9 kg/m2) but not in the highest BMI group (P=0.33).

The researchers noted the study's cross-sectional design as a limitation, as they were not able to assess any causal relationship between height and BMI on glucose tolerance. However, they noted that these results may have several clinical implications.

For instance, the authors suggested that adjusting for height and BMI may allow clinicians to better interpret results of oral glucose tolerance testing in people with a BMI less than 35 kg/m2. They added that a uniform oral glucose load may be inadequate to accurately assess glucose tolerance, as well as that any given elevation of two-hour plasma glucose in a tall person (with BMI <35 kg/m2) may indicate a more severe metabolic disturbance than in a shorter person.

The differing results for people in the highest BMI category may indicate that increased adiposity slowly transforms a person's response to oral glucose tolerance testing into a physiological one, “meaning that eventually no ‘height-related response’ remains, and an ‘obesity-related physiological response’ over-rides this,” the study authors posited.