Low Vitamin D Levels Linked to Prediabetes and Prehypertension

A recently published study showed that adults with low vitamin D levels had more than double the risk of prehypertension and prediabetes than adults with higher vitamin D levels.

Prediabetes and prehypertension have been associated with low vitamin D levels. In a recent issue of the journal Diabetes Care, scientists report a correlation between reduced vitamin D levels and prediabetes and prehypertension in adults. Both prediabetes and prehypertension are estimated to exist in at least one-fourth of disease-free adults. 

Researchers analyzed data from 898 men and 813 women who participated in the National Health and Nutrition Examination Survey (NHANES), 2001-2006. Blood pressure measurements were obtained during examinations conducted upon enrollment, and blood samples were evaluated for glucose, serum 25-hydroxyvitamin D and other factors.


Prediabetes was defined as having a fasting serum glucose of between 100 and 125 milligrams per deciliter, and prehypertension was defined as systolic blood pressure of 120 to 139 mmHg and/or diastolic blood pressure between 80 and 89 mmHg. Prediabetes was 33 percent higher among those with vitamin D levels of 76.3 nmol/l (30.5 ng/ml) or less compared to those with higher levels. Prehypertension was evident in 61 percent of those with the lower vitamin D levels. Participants with undiagnosed diabetes and untreated hypertension had even lower vitamin D levels on average. Serum vitamin D levels tended to decline with increasing age and body mass.

When the risk of having both conditions was considered, those with low vitamin D levels had 2.4 times the risk of that experienced by subjects with higher vitamin D levels.  

It is reasonable that among those with prediabetes or prehypertension, vitamin D supplementation resulting in increased serum vitamin D levels may help reverse subtle changes in fasting serum glucose and resting blood pressure that may lead to more advanced disease states. 

Alok K. Gupta, MD, Meghan M. Brashear, MPH and William D. Johnson, PHD. Prediabetes and Prehypertension in Healthy Adults Are Associated With Low Vitamin D Levels. Diabetes Care March 2011 vol. 34 no. 3 658-660.

Glycemic Load is a Better Predictor of Glycemic Response Than Carbohydrate Content Alone

A new study provides evidence that the glycemic load of a meal is a better predictor of blood glucose and insulin response that simply accounting for total carbohydrates.

The glycemic load (GL) is a ranking system for carbohydrate content in food portions based on their glycemic index (GI) and the portion size. Glycemic load for a single serving of a food can be calculated as the quantity (in grams) of its carbohydrate content, multiplied by its GI, and divided by 100. While GL is increasingly used in nutritional research, its ability to predict postprandial (after meal) blood glucose and insulin response for a wide range of foods or mixed meals has been unclear.   

In a recent issue of the American Journal of Clinical Nutrition, researchers sought to assess the degree of correlation between calculated GL and observed glucose and insulin responses in healthy subjects consuming calorically identical portions of single foods and mixed meals.

In study 1, healthy subjects consumed 240 calorie portions of 121 single foods in 10 food categories. In study 2, healthy subjects consumed 480 calorie servings of 13 mixed meals. Foods and meals varied widely in macronutrient content, fiber, and GL. Blood glucose and insulin responses were measured and compared to a reference food (= 100).

Among the single foods, GL was a more powerful predictor of postprandial glucose and insulin response than was the available carbohydrate content itself. Similarly, for mixed meals, GL was also the strongest predictor of postprandial glucose and insulin responses. Carbohydrate content alone was predictive of the glucose and insulin responses to single foods, but not to mixed meals.

The results of this study are the first to provide large-scale evidence of the superiority of using dietary GL over carbohydrate content alone to estimate postprandial glucose and insulin response in healthy individuals.   

Jiansong Bao et al. Prediction of postprandial glycemia and insulinemia in lean, young, healthy adults: glycemic load compared with carbohydrate content alone. Am J Clin Nutr May 2011 vol. 93 no. 5 984-996.

Energy Expenditure is Reduced by Sleep Deprivation – A Possible Link to Obesity

A new study shows that total sleep deprivation reduces energy expenditure and may partly explain the connection between poor sleep and an increased risk of obesity.

Observational and epidemiologic evidence has shown that chronic deficits in sleep are related to an increased risk of obesity, but the mechanisms behind this relation have not been fully explained.   

In a recent study published in the American Journal of Clinical Nutrition researchers examined the effect of a single night of total sleep deprivation on food intake and morning energy expenditure.

Using a balanced crossover design, scientists examined 14 healthy, normal-weight males on 2 occasions during a regular 24 hour sleep-wake cycle (including 8 hours of nocturnal sleep) and a 24 hour period of continuous wakefulness. On the morning after regular sleep and total sleep deprivation, resting and postprandial (after meal) energy expenditures were analyzed.  Food intake in both groups was assessed again in the late afternoon after the subjects were given a free-choice food intake from a large buffet. Circulating concentrations of ghrelin, leptin, norepinephrine, cortisol, thyreotropin, glucose, and insulin were repeatedly measured over the entire 24 hour session.

In comparison with normal sleep, resting energy expenditure was reduced by 5% and postprandial expenditure by 20% in the sleep deprived subjects.  Nocturnal wakefulness increased morning plasma ghrelin concentrations (a hormone that stimulates hunger), and nocturnal and daytime circulating concentrations of thyreotropin, cortisol, and norepinephrine) as well as morning postprandial plasma glucose concentrations. Changes in food intakes were variable, and no differences between wake and sleep conditions were detected.   

These research findings show that one night of sleep deprivation significantly reduces energy expenditure in the short-term, which suggests that sleep contributes to the regulation of daytime energy expenditure in humans.  

Christian Benedict et al. Acute sleep deprivation reduces energy expenditure in healthy men Am J Clin Nutr June 2011 vol. 93 no. 6 1229-1236.