Inadequacy of Vitamin D Nutritional Status in Individuals with Metabolically Unhealthy Obesity Phenotype: The Relevance of Insulin Resistance

Relationship between the thrombospondin-1/Toll-like receptor 4 (TSP1/TLR4) pathway and vitamin D levels in obese and normal weight subjects with different metabolic phenotypes

Thrombospondin-1 (TSP1) contributes to obesity-associated inflammation via activating Toll-like receptor 4 (TLR4). The regulatory role of vitamin D on this pathway has been suggested. This study aimed to investigate the relationship between TSP1/TLR4 pathway and vitamin D in obese and normal weight subjects with different metabolic phenotypes. Thirty obese and thirty normal weight men were selected. Anthropometric parameters and serum TSP1, TLR4, TNF-α, vitamin D, and metabolic profile were determined. Metabolic phenotypes of obese and normal weight subjects were determined. Findings revealed enhanced TSP1/TLR4/TNF-α levels and reduced 25(OH)D levels in obese compared to normal weight subjects and metabolically unhealthy compared to metabolically healthy subjects. TSP1 correlated positively with parameters of unhealthy metabolic profile. TSP1, TLR4 and TNF-α levels significantly negatively correlated with vitamin D levels. In conclusion, vitamin D might exert a regulatory role on TSP1/TLR4 pathway, providing a potential mechanism that links hypovitaminosis D with risk of metabolic dysfunction.

Vitamin D in atherosclerosis and cardiovascular events

Both experimental and clinical findings linking vitamin D to cardiovascular (CV) risk have prompted consideration of its supplementation to improve overall health. Yet several meta-analyses do not provide support for the clinical effectiveness of this strategy. Meanwhile, the understanding of the roles of vitamin D in the pathophysiology of CV diseases has evolved. Specifically, recent work has revealed some non-classical pleiotropic effects of vitamin D, increasing the complexity of vitamin D signalling. Within particular microenvironments (e.g. dysfunctional adipose tissue and atherosclerotic plaque), vitamin D can act locally at cellular level through intracrine/autocrine/paracrine feedforward and feedback circuits. Within atherosclerotic tissues, 'local' vitamin D levels may influence relevant systemic consequences independently of its circulating pool. Moreover, vitamin D links closely to other signalling pathways of CV relevance including those driving cellular senescence, ageing, and age-related diseases-among them CV conditions. This review updates knowledge on vitamin D biology aiming to clarify the widening gap between experimental and clinical evidence. It highlights the potential reverse causation confounding correlation between vitamin D status and CV health, and the need to consider novel pathophysiological concepts in the design of future clinical trials that explore the effects of vitamin D on atherosclerosis and risk of CV events.

Dietary determinants of healthy/unhealthy metabolic phenotype in individuals with normal weight or overweight/obesity: a systematic review

Objectives: Nutritional factors are amongst the major determinants in the onset and development of obesity and metabolic complications. Nevertheless, the dietary determinants of metabolic health are not completely elucidated. The aim of this systematic review is to investigate nutritional and dietary factors that may contribute to metabolic heterogeneity in individuals with obesity or normal weight. Methods: A literature search was performed in PubMed, Scopus, EMBASE, and google scholar databases until August 2021, to locate studies that examined metabolic health and its association with intakes of specific foods or food groups, nutrient intakes or status, as well as adherence to certain dietary patterns. Two researchers had independently screened titles and abstracts, examined full-text studies, conducted data extraction, and evaluated their quality using the Newcastle-Ottawa Scale. Results: Twenty-seven studies, with a total of 39518 subjects, were included. Of these studies, 11 articles evaluated the association between different dietary patterns and metabolic phenotypes, while 15 had investigated the association of single food/nutrients intakes or nutrient status with metabolic phenotype, and one paper evaluated the association of dietary inflammatory index with metabolic health. The findings of these studies propose that healthy dietary patterns such as the Mediterranean pattern, Dietary Approaches to Stop Hypertension, and population-derived patterns (such as the "Healthy" and "Fruit and vegetable" patterns) were associated with higher odds of the metabolically healthy phenotype. Higher intakes of fruits, vegetables, dairy products, coffee/tea, vitamin D, magnesium, and flavonoids, were suggested to lower the risk of developing metabolically unhealthy phenotype, while, higher consumption of saturated fat, carbohydrate and sugar-sweetened beverages, fast foods, organ meats, and a pro-inflammatory diet increased the risk. Conclusion: Results from published studies, which were mostly cross-sectional, suggest that higher adherence to unhealthier dietary patterns, characterized by the consumption of refined and processed foods, was associated with a lower likelihood of having a healthy metabolic phenotype, while the opposite was observed for healthier dietary patterns. Findings may be used in developing nutritional strategies aimed at improving metabolic health in the population.