Basal metabolic rate and thyroid hormones of late-middle-aged and older human subjects: the ZENITH study

Predictive Roles of Basal Metabolic Rate and Muscle Mass in Lung Function among Patients with Obese Asthma: A Prospective Cohort Study

BACKGROUND

The metabolic-status-related mechanisms underlying the deterioration of the lung function in obese asthma have not been completely elucidated.

OBJECTIVE

This study aimed to investigate the basal metabolic rate (BMR) in patients with obese asthma, its association with the lung function, and its mediating role in the impact of obesity on the lung function.

METHODS

A 12-month prospective cohort study (n = 598) was conducted in a real-world setting, comparing clinical, body composition, BMR, and lung function data between patients with obese (n = 282) and non-obese (n = 316) asthma. Path model mediation analyses for the BMR and skeletal muscle mass (SMM) were conducted. We also explored the effects of the BMR on the long-term lung function in patients with asthma.

RESULTS

Patients with obese asthma exhibited greater airway obstruction, with lower FEV1 (1.99 vs. 2.29 L), FVC (3.02 vs. 3.33 L), and FEV1/FVC (65.5 vs. 68.2%) values compared to patients with non-obese asthma. The patients with obese asthma also had higher BMRs (1284.27 vs. 1210.08 kcal/d) and SMM (23.53 vs. 22.10 kg). Both the BMR and SMM mediated the relationship between obesity and the lung function spirometers (FEV1, %FEV1, FVC, %FVC, and FEV1/FVC). A higher BMR or SMM was associated with better long-term lung function.

CONCLUSIONS

Our study highlights the significance of the BMR and SMM in mediating the relationship between obesity and spirometry in patients with asthma, and in determining the long-term lung function. Interventions for obese asthma should focus not only on reducing adiposity but also on maintaining a high BMR.

Relation Between Zinc and Thyroid Hormones in Humans: a Systematic Review

The aim of this study was to systematically evaluate the relation between zinc and the thyroid hormones in humans. The search for articles was conducted using the Pubmed, Scopus, Cochrane Central Register of Controlled Trials (CENTRAL), and ScienceDirect databases on October 21 and 22, 2019, by two authors independently. The recommendations of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) were followed in the conduct of this review. The Cochrane Collaboration tool was used to assess the risk of bias of the trials included in this review. After the screening of the articles, eight studies that assessed the effects of zinc supplementation on thyroid hormone concentrations and ten studies that assessed the relationship between blood zinc concentrations and thyroid hormones were included in this systematic review. Although cross-sectional and case-control studies have shown a relationship between zinc deficiency and thyroid, the data from this systematic review provides inconclusive evidence with respect to the effects of zinc supplementation on thyroid hormone concentrations due to the divergence of the research found by the authors that only reports findings in patients suffering from some kind of disease, which cannot be generalized to the average human population.

Environmental Factors Affecting Thyroid-Stimulating Hormone and Thyroid Hormone Levels

Thyroid hormones are necessary for the normal functioning of physiological systems. Therefore, knowledge of any factor (whether genetic, environmental or intrinsic) that alters the levels of thyroid-stimulating hormone (TSH) and thyroid hormones is crucial. Genetic factors contribute up to 65% of interindividual variations in TSH and thyroid hormone levels, but many environmental factors can also affect thyroid function. This review discusses studies that have analyzed the impact of environmental factors on TSH and thyroid hormone levels in healthy adults. We included lifestyle factors (smoking, alcohol consumption, diet and exercise) and pollutants (chemicals and heavy metals). Many inconsistencies in the results have been observed between studies, making it difficult to draw a general conclusion about how a particular environmental factor influences TSH and thyroid hormone levels. However, lifestyle factors that showed the clearest association with TSH and thyroid hormones were smoking, body mass index (BMI) and iodine (micronutrient taken from the diet). Smoking mainly led to a decrease in TSH levels and an increase in triiodothyronine (T3) and thyroxine (T4) levels, while BMI levels were positively correlated with TSH and free T3 levels. Excess iodine led to an increase in TSH levels and a decrease in thyroid hormone levels. Among the pollutants analyzed, most studies observed a decrease in thyroid hormone levels after exposure to perchlorate. Future studies should continue to analyze the impact of environmental factors on thyroid function as they could contribute to understanding the complex background of gene-environment interactions underlying the pathology of thyroid diseases.

Nutrition for Older Athletes: Focus on Sex-Differences

Regular physical exercise and a healthy diet are major determinants of a healthy lifespan. Although aging is associated with declining endurance performance and muscle function, these components can favorably be modified by regular physical activity and especially by exercise training at all ages in both sexes. In addition, age-related changes in body composition and metabolism, which affect even highly trained masters athletes, can in part be compensated for by higher exercise metabolic efficiency in active individuals. Accordingly, masters athletes are often considered as a role model for healthy aging and their physical capacities are an impressive example of what is possible in aging individuals. In the present review, we first discuss physiological changes, performance and trainability of older athletes with a focus on sex differences. Second, we describe the most important hormonal alterations occurring during aging pertaining regulation of appetite, glucose homeostasis and energy expenditure and the modulatory role of exercise training. The third part highlights nutritional aspects that may support health and physical performance for older athletes. Key nutrition-related concerns include the need for adequate energy and protein intake for preventing low bone and muscle mass and a higher demand for specific nutrients (e.g., vitamin D and probiotics) that may reduce the infection burden in masters athletes. Fourth, we present important research findings on the association between exercise, nutrition and the microbiota, which represents a rapidly developing field in sports nutrition.

Development of new predictive equations for basal metabolic rate in Iranian healthy adults: negligible effect of sex

Some studies have reported inaccuracy of predicting basal metabolic rate (BMR) by using common equations for Asian people. Thus, this study was undertaken to develop new predictive equations for the Iranian community and also to compare their accuracy with the commonly used formulas. Anthropometric measures and thyroid function were evaluated for 267 healthy subjects (18-60 y). Indirect calorimetry (InCal) was performed only for those participants with normal thyroid function tests (n = 252). Comparison of predicted RMR (both kcal/d and kcal.kg.wt^-1.d^-1) using current predictive formulas and measured RMR revealed that Harris-Benedict and FAO/WHO/UNU significantly over-estimated and Mifflin-St. Jeor significantly under-estimated RMR as compared to InCal measurements. In stepwise regression analysis for developing new equations, the highest r² (=0.89) was from a model comprising sex, height and weight. However, further analyses revealed that unlike the subjects under 30 y, the association between age and the measured RMR in subjects 30 y and plus was negative (r = -0.241, p = 0.001). As a result, two separate equations were developed for these two age groups. Over 80 percent of variations were covered by the new equations. In conclusion, there were statistical significant under- and over-estimation of RMR using common predictive equations in our subjects. Using the new equations, the accuracy of the calculated RMR increased remarkably.

Fat-free mass and calf circumference as body composition indices to determine non-exercise activity thermogenesis in patients with diabetes

Aims/Introduction

To investigate the clinical and anthropometrical parameters that are associated with non‐exercise activity thermogenesis that is composed of basal energy expenditure (BEE) and diet‐induced thermogenesis (DIT) in patients with diabetes.

Materials and Methods

Body composition was assessed using bioelectrical impedance, and BEE and DIT were measured using indirect calorimetry in 40 Japanese patients with diabetes.

Results

BEE correlated positively with bodyweight, body mass index, fat mass, and fat‐free mass, and correlated negatively with age in both men and women. In multivariate logistic regression analysis, BEE correlated positively with both fat mass and fat‐free mass independently of sex and age. In addition, DIT correlated positively with bodyweight, body mass index, fat mass and fat‐free mass, and correlated negatively with age in women, but not men. Fat‐free mass contributed to DIT at least partly, and an aging‐related decrease in DIT was observed. The best anthropometric parameter that reflected fat mass and fat‐free mass was hip circumference (HC) and calf circumference (CC), respectively, in both men and women. Indeed, both HC (men β = 0.600, P < 0.001; women β = 0.752, P < 0.001) and CC (men β = 0.810, P = 0.012; women β = 0.821, P = 0.002) were correlated with BEE independently of age and sex. In addition, CC (β = 0.653, P = 0.009), but not HC was correlated with DIT significantly only in females, independently of age.

Conclusions

HC reflects fat mass and was positively associated with BEE, but not with DIT. In contrast, CC reflects fat‐free mass, and was positively associated with BEE in both men and women, and with DIT in women.

The impact of common micronutrient deficiencies on iodine and thyroid metabolism: the evidence from human studies

Deficiencies of micronutrients are highly prevalent in low-income countries. Inadequate intake of iodine impairs thyroid function and results in a spectrum of disorders. Other common deficiencies of micronutrients such as iron, selenium, vitamin A, and possibly zinc may interact with iodine nutrition and thyroid function. Randomised controlled intervention trials in iodine- and iron-deficient populations have shown that providing iron along with iodine results in greater improvements in thyroid function and volume than providing iodine alone. Vitamin A supplementation given alone or in combination with iodised salt can have a beneficial impact on thyroid function and thyroid size. Despite numerous studies of the effect of selenium on iodine and thyroid metabolism in animals, most published randomised controlled intervention trials in human populations failed to confirm an impact of selenium supplementation on thyroid metabolism. Little evidence is available on interactions between iodine and zinc metabolism.

Effect of zinc supplementation on thyroid hormone function. A case study of two college females

BACKGROUND/AIMS

Zinc is crucial for proper thyroid hormone metabolism; zinc deficiency may result in decreased thyroid hormone levels and resting metabolic rate (RMR). The purpose of this investigation was to assess the effects of zinc supplementation on plasma zinc, serum ferritin, plasma total triiodothyronine (T(3)) and thyroxine (T(4)), serum free T(3) and T(4), and thyroid-stimulating hormone concentrations, and RMR in zinc-deficient, physically active women.

METHODS

Two zinc-deficient female college students (ZD1 and ZD2) were supplemented with 26.4 mg/day of zinc (as zinc gluconate), and the above parameters were analyzed at 0, 2 and 4 months.

RESULTS

Zinc deficiency was clinically corrected in both subjects, while serum ferritin concentration declined to classify both subjects as borderline iron deficient (ZD1 = 15.3 and ZD2 = 15.3 ng/ml at 4 months). At 4 months, total T(3) concentrations increased in ZD1, while all thyroid hormone concentrations increased in ZD2. RMR increased in both subjects by 4 months.

CONCLUSION

Zinc supplementation appeared to be directly responsible for the increase in plasma zinc and decline in serum ferritin concentrations in both subjects. Zinc supplementation appeared to have a favorable effect on thyroid hormone levels, particularly total T(3), and RMR.

The endeavor of high maintenance homeostasis: resting metabolic rate and the legacy of longevity

Metabolism, the continuous conversion between structural molecules and energy, is life in essence. Size, metabolic rate, and maximum life span appear to be inextricably interconnected in all biological organisms and almost follow a "universal" law. The notion of metabolic rate as the natural "rate of living" filled most of the academic discussion on aging in the early 20th century to be later replaced by the free-radical theory of aging. We argue that the rate of living theory was discarded too quickly and that studying factors affecting resting metabolic rate during the aging process may provide great insight into the core mechanisms explaining differential longevity between individuals, and possibly the process leading to frailty. We predict that measures of resting metabolic rate will be introduced in geriatric clinical practice to gather information on the degree of multisystem dysregulation, exhaustion of energy reserve, and risk of irreversible frailty.