Micronutrients work as coenzymes, cocatalysts, and buffers and are essential for various cellular and biochemical processes, such as releasing energy for synthesis, movement, and other processes. ¹ Due to their impact on intracellular homocysteine concentration and oxidative stress, subclinical deficiencies in several micronutrients have the potential to significantly slow the development of chronic disease. ² When the consumption of a micronutrient falls below the current recommended dietary amount, a significant chronic metabolic disturbance may result from the nutrient deficiencies such as polycystic ovarian syndrome (PCOS), insulin resistance, obesity, and metabolic syndrome. ^{3 – 5} In recent years, many studies approved that nutrients could play a vital role in obesity and metabolic syndrome prevention. Also, energy-dense foods with deficit nutrients contribute to the development of obesity, metabolic syndrome, and inflammation. ^{4 , 6}

B vitamins play a crucial role in the balance and metabolism of energy. ⁷ Energy metabolism mainly benefits from the B-complex vitamins. Specifically, decarboxylation, transamination, acylation, oxidation, and reduction of substrates that are ultimately employed in energy intake require thiamin, riboflavin, niacin, and vitamin B6. One or more of these are also necessary for synthesizing steroids, fatty acids, cholesterol, amino acids, and glucose. ⁸ B-vitamin deficiency may impact energy metabolism, and cause insulin resistance, chronic inflammation, obesity, and elevated oxidative stress, which may contribute to the pathophysiology of metabolic syndrome. ^{9 , 10} B-vitamin deficiency has been approved in individuals with obesity and metabolic syndrome. ^{2 , 11} Moreover, thiamin (B1) and riboflavin (B2) intake are inversely associated with body mass index (BMI). ^{2 , 7} As energy metabolism may be affected by deficiencies in biotin, niacin (B3), folate, and vitamins B6 and B12, which may enhance the generation of reactive oxidants and inflammatory reactions, lipogenesis may also be promoted, which may increase obesity. ^{12 , 13} Additionally, B vitamins play a vital role (methyl group donor and act as a coenzyme) in DNA methylation, which is important for body adiposity regulation ¹⁴ and is associated with BMI. ¹⁵

Wu et al., ⁶ suggested that a higher intake of vitamins B1, B2, B3, B6, and dietary folate were associated with a reduced risk of metabolic syndrome. Also, numerous cardiovascular diseases (CVDs), and risk factors, such as type 1 and type 2 diabetes, obesity, chronic vascular inflammation, dyslipidemia, heart failure, myocardial infarction, and depression, have been linked to B1, B3, and B6 deficiency. ^{11 , 16}

Dietary intake of B vitamins has been found to be inversely related to CVD, as their attribution in lowering CVD risk factors, such as plasma homocysteine, serum triglycerides, and C-reaction protein. ¹⁷ These risk factors have been linked to the atherosclerotic process ¹⁸ and endothelial dysfunction, ¹⁹ which engage in CVD development. B vitamins play a role in the metabolism of one carbon unit, therefore each of these nutrients may have an impact on the pathological development of CVD by reducing homocysteine concentrations, methylation processes, and oxidative stress. ^{20 , 21}

Furthermore, nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP) are redox mediator coenzymes that are precursors of B3, ²² which has also been demonstrated to enhance levels of high-density lipoprotein cholesterol (HDL), lower levels of triglycerides (TG), very low levels of low-density lipoprotein cholesterol (VLDL-C), and dramatically diminish the risk of CVD and the progression of atherosclerosis. ²³ Based on the aforementioned, not enough data are available to cover the association between energy-releasing vitamins with indices of obesity and cardiac function. So, this study aimed to assess the impact of energy-releasing B-vitamins intake (B1, B2, B3, and B6) on selected indices of obesity and cardiac function.

Obesity is considered to be one of the malnutrition forms, which develops individually and as a result of unbalanced nutrition. ² Based on The World Health Organization (WHO), obesity is defined as the “double burden of malnutrition” and indicates that it may occur more frequently in socioeconomically underdeveloped and poorly nourished societies side by side with malnutrition, and in consequence, chronic diseases may develop. ³³ Vitamins B1 (thiamine), B2 (Riboflavin), B3 (niacin), and B6 (pyridoxine), all of which are vital for the metabolism of energy, carbohydrate, lipid, and amino acid, as well as the regulation of the cellular redox state. ¹¹ Some studies have revealed that obesity is associated with low levels of fruit intake, total diet quality, and micronutrient intake compared to normal BMI, which means that people living with obesity may consume fewer micronutrients due to the foods they eat and subsequently may lead to low levels of water-soluble vitamins. ^{11 , 34} Also, it has been found that the requirements of B vitamins has been increased for people with obesity, diabetes, and peripheral neuropathy. ^{35 , 36}

The current study studied the association between dietary intake of B vitamins; specifically, B1, B2, B3, and B6, with indices of obesity and cardiac function were studied. Among these B vitamins, B1 and B6 had a significant association with some of the obesity indices; B2 with BAI indices, and B6 had a significant association with LAP (one of the cardiac function indices) The result revealed that the score of obesity indices CI and AVI decreased with an increase in the dietary intake of vitamin B1. Moreover, the energy-adjusted intake of B1 had a significantly inverse weak correlation with AVI and BRI among the total sample and male participants. Energy-adjusted B1 vitamin significantly explained 2.43% of changes observed in the AVI and 1.24% of changes observed in the BRI indices ( p < 0.05). In addition, based on this study result, increasing the intake of B6 led to reductions in the score of obesity (CI, AVI, BRI, WWI) and cardiac function indices (LAP and AIP).

By these results, Kerns et al., reported that 15.5–29% of patients with obesity who seek bariatric surgery have malnutrition disease, specifically, B1 deficiency. ³⁷ In line with the present findings, B1 deficiency was found in children with obesity, and most of those cases were subclinical. ³⁸ Kardas et al., observed significantly decreased levels of vitamin B2, vitamin B12, and B9 in the obesity and metabolic syndrome groups. ² By contrast, they observed an increased level of B1 with a positive correlation with LDL-C and a negative correlation with HOMA-IR and body weight in the target group. ² Studies show that vitamin B2 deficiency causes functional alterations in adipocytes, and thus has pro-inflammatory and proinsulin effects, resulting from increased adipocytes. ³⁹ Moreover, in the subjects with obesity, an inverse correlation was found between vitamin B6 and body weight. ² Gunanti et al. (2014) examined the associations between serum B vitamins and vitamin intake with body fat in Mexican American children aged 8–15 years. B1 and B2 intakes were inversely associated with BMI and trunk fat mass (b:21.26, p < 0.05; b: 21.37, p < 0.05). ⁷ Different suggested mechanisms have been introduced to describe the correlation between B-vitamin deficiency and obesity occurrence, all are summarized in Figure 1. The interaction mechanism between the reduced serum B-complex level and obesity includes the reduction in B1, B2, B3, and B6 levels associated with an increased risk of metabolic syndrome, which is considered one of the major cases of obesity. ⁶ Also, decreases in the levels of B1 and B2 are correlated with increased BMI, ⁷ and B6 regulates the expression of peroxisome proliferator-activated receptor gamma (PPARγ), which is a target gene that plays a key role in adipocyte gene expression and adipogenesis. ¹³ Additionally, decreased B1, B3, and B6 concentrations correlate significantly with an increased risk of insulin resistance, metabolic dysfunction, and obesity. ⁴⁰ Moreover, generally, B vitamins have a fundamental role in the lipid and lipoprotein metabolism cascade. Therefore, quantitative or qualitative defects in B vitamins will negatively impact the metabolism of lipid derivatives. ⁴¹ Also, B2 plays a vital role in energy-expenditure adipocyte gene regulation at the epigenetic level. ⁴² The final suggested mechanism is that increased body weight leads to the reduction of vitamin B6 levels by inducing systemic oxidative stress, which leads to stimulating adipocytokines dysregulation. ^{7 , 23}

Studies investigating the prevalence of B1 deficiency among patients with cardiovascular diseases (CVDs) concluded that B1 deficiency could have a role in the development of CVDs. ¹⁶ Odum et al. (2012) found that the mean plasma vitamins B1, B3, B6 and C concentrations of subjects with metabolic syndrome were significantly lower than that of controls ( p = 0.001, 0.05, 0.045, 0.001, respectively). Also, 14% and 32% of subjects had inadequate vitamin B1 and vitamin C status, respectively. ¹¹ Additionally, Wu et al., found a linear inverse relationship between dietary vitamin B1, niacin, B6, and metabolic syndrome, and a non-linear inverse relationship was found between dietary vitamin B2 and metabolic syndrome. ⁶ It was noted that vitamin B6 supplementation is vital in preventing metabolic syndrome and pyridoxine levels were lower in patients with metabolic syndrome compared to those in healthy patients. ⁴² They suggested that a higher intake of vitamin B1, B2, niacin, B6, and dietary folate equivalent was associated with a reduced risk of metabolic syndrome. ⁶ Not like other results, Kardas et al., found that B1 levels were high in subjects with obesity and metabolic syndrome; they explained this difference by the fact that these individuals typically consumed large quantities of bread and cereals, which are considered major sources of B1. ² Many suggested mechanisms have been introduced to describe the association between B-vitamin deficiency and metabolic syndrome and coronary heart diseases, all are summarized in Figure 2.

B3 intake is suggested to decrease serum levels of LDL, VLDL, and TG, as well as, increase levels of HDL. ^{20 , 23} Also, vitamins B2 and B6 have a vital role in homocysteine demethylation into methionine, which leads to decreased risk of atherosclerosis. ^{14 , 20} Additionally, B6 is associated with a reduced risk of metabolic syndrome. ⁶ Lastly, low levels of B1, B3, and B6 are associated with increased insulin resistance, metabolic dysfunction, and increased risk of atherosclerosis, obesity, metabolic syndrome, diabetes, and cardiovascular disease. ^{11 , 43}

This study is one of the early studies that placed importance on examining the relationship between inadequate dietary intake of energy-releasing B-vitamins, and each of the indices of obesity and cardiac function in healthy individuals. There are not enough studies that clarify the correlation between B vitamins and indices of obesity and cardiac function. This provides the scope to highlight the significance of dietary consumption and the part that nutritional inadequacies play in the prevalence of obesity and heart disease.

The present study had certain limitations. First, because the study was cross-sectional, it was impossible to conclusively establish a causal link between obesity, cardiac function indices, and dietary intake of B vitamins. The availability of both conventional and innovative anthropometric measures as well as cardiac function indices is one of our study’s key strengths. Additionally, because the current data were gathered before the COVID-19 pandemic, they can be used to compare studies done before and after the pandemic by researchers in the same field. Another key benefit of the study is the originality of its investigation of the relationship between indicators of cardiac function and several chosen nutrients. We selected a representative sample size to prevent sample bias, which was calculated based on the total Jordanian population using online software. Also, the incomplete anthropometric measurements and/or biochemical data have been excluded to eliminate information bias. However, there were no self-reporting data to bypass recall bias, the interviewers were trained for data collection.

In conclusion, after energy adjustment, obesity indices are inversely associated with B1, B2, and B6 vitamins. Specifically, AVI and BRI were inversely associated with B1 and B6 vitamins, whereas BAI was inversely associated with B2 vitamins among female participants. Only the B6 vitamin was inversely associated with LAP and AIP among cardiac function indices. Increasing the intake of these vitamins (B1, B2, and B6) results in reducing the score of obesity (CI, AVI, BRI, WWI) and cardiac function indices (LAP and AIP), which in consequence may help reduce the occurrence of obesity and related coronary diseases.