Vitamin D Supplementation Increases the Aerobic Training Effects on Anthropometric Indices in Elderly Women with Non-Alcoholic Fatty Liver Disease and Vitamin D Deficiency

Non-alcoholic fatty liver disease (NAFLD) is a type of common, chronic, and progressive fatty liver disease (1). It is similar to alcoholic fatty liver disease, with the exception that there is no alcohol abuse (2). The prevalence of NAFLD is reported between 3% and 25% in the general populations of different countries (3), 20% to 30% in developing countries (4), and more than 34% in adults in the United States (5). Although the exact causes of NAFLD are still unknown, the results of available studies indicate that there is a strong association between NAFLD and sedentary lifestyle, inappropriate nutrition, obesity, type 2 diabetes, and increased free fatty acids that may increase excess fat building up in the liver, resulting in new liver lipogenesis and beta-oxidation disorders (3, 6). In addition, increasing age causes both structural and functional undesirable alterations in the liver (7). As the liver volume decreases, the first phase of drug metabolism drops off gradually in the liver, the expression of various types of proteins alters, and hepatobiliary function decreases (8). In women, in addition to the mentioned causes, the menopause period leads to adverse changes in body composition and lipid distribution, which increases the risk of coronary artery disease (CAD) and NAFLD (9).

Nowadays, weight loss is recognized as the only definitive treatment for NAFLD and lifestyle intervention is the only part of its management. Physical activity and diet can potentially contribute to weight loss and subsequently, liver fat reduction although it is difficult to achieve and maintain the optimal weight (10). After 16 weeks of treadmill training, Kawanishi et al. reported increased liver fat and plasma alanine aminotransferase (ALT) activity in rats with NAFLD consuming a high-fat/high-sugar diet, while the control group showed liver damage (11). Another study showed that eight weeks of aerobic training and regular endurance training were effective in NAFLD (12). However, there are some conflicting results. Devries et al. noted that 12-week endurance training did not have a significant effect on liver fat and ALT concentration; in addition, endurance training had no positive effect on liver fat and enzymes in obese people (13).

Vitamin D deficiency has recently been reported in many countries (14, 15). Its prevalence in Iran is 47.85% in women and 34.75% in men (16, 17). The higher prevalence of vitamin D deficiency is associated with a greater prevalence of obesity in the world (18, 19). Recent epidemiological studies also show that low levels of serum vitamin D are associated with NAFLD (20). Vitamin D deficiency impairs the function of various cells, including the endocrine systemand pancreas, by altering the metabolites function (21). Therefore, vitamin D supplementation can be effective in reducing vitamin D deficiency and its associated complications, especially in countries such as Iran with no implemented vitamin D fortification program. A national health and nutrition assessment on 1287 adult participants disclosed that patients with NAFLD and elevated levels of ALT had decreased levels of 25 hydroxyvitamin D (25-OHD) (22). The results of some cross-sectional studies indicate an inverse relationship between 25-OHD levels and anthropometric indices (23, 24). Rocha et al. evaluated the association of undesirable anthropometric indices in 81 patients with NAFLD and reported that body mass index and waist circumferences were highly associated with insulin resistance and metabolic syndrome (25). Moreover, it is known that waist circumference WC and dorsocervical lipohypertrophy (DCL) are the predictors of metabolic risk profile and NAFLD and they are strongly associated with the severity of steatohepatitis. In addition, WC and BMI doubled the contribution of DCL to the severity of nonalcoholic steatohepatitis (26). Limited clinical trials have studied the interaction effect of aerobic training and vitamin D supplementation while it is important to improve anthropometric indices, liver enzymes and glycemic indexes in NAFLD.

We aimed to evaluate the interaction effect of aerobic training and vitamin D on anthropometric indices in elderly women with NAFLD and vitamin D deficiency.

The demographic data and anthropometric indices of the participants and their between-group comparison are presented in Table 2. After eight weeks, there were significant decreases in BW, BMI, BFP, and WHR in the AT + Vit. D, AT, and Vit. D groups. However, the C group showed significant increases in BW, BMI, BFP, and WHR levels (Table 2). The results of one-way ANOVA showed no significant difference in BW, BMI, BFP, and WHR between the groups at pretest; however, significant differences were observed at posttest (Table 2).

The results of Tukey’s post hoc test showed that the lowest anthropometric indices (BW, BMI, PBF, and WHR) were observed in the AT + Vit. D group. No significant difference was seen in BW, BFP, BMI, and WHR between the A + Vit. D, AT, and Vit. D groups; however, the mentioned variables were significantly higher in the control group than in other groups at posttest (Table 2).

Substantial evidence indicates that physical activity is the first-line treatment of obesity and is a management approach for obesity-related mortality and morbidity. The results of the study indicated that aerobic training alone reduced BW, BMI, BFP, and WHR; however, more reductions were observed when aerobic training was accompanied by vitamin D supplementation. Based on the results of the studies, aerobic training is associated with improvements in cardiovascular risk factors, including improved insulin resistance and weight loss (28, 29). Swift et al. found that regular exercise training increased the expression of lipolytic enzymes, the density of mitochondria, and the recruitment of fat cells instead of carbohydrates for energy demand while reduced body fat, leading to consequent reductions in BW, BMI, and BFP (30). On the other hand, the increase in anthropometric indices (BW, BMI, and WHR) is an indicator of visceral fat accumulation that has a high correlation with liver fat accumulation in NAFLD (31). Visceral fat tissues are more resistant to insulin; therefore, it might stimulate lipolysis and call for free fatty acids in the bloodstream, which is an influential factor in the accumulation of more triglycerides in the liver (32). In addition regular aerobic training is known to increase the daily energy expenditure, increase the oxidation of lipids in skeletal muscles and mitochondria of hepatocytes, and reduce the obesity, especially the abdominal obesity; they may consequently lead to reduced visceral fat, free fatty acid transfusion into the liver, and fat deposition in the liver, along with the increased fat oxidation in the liver (33, 34).

The findings of the study also showed that Vit. D alone reduced BW, BMI, and BFP. Studies report an association between vitamin D deficiency and the prevalence of chronic diseases (35, 36). Limited studies have been conducted on the relationship between vitamin D intake and BW, BMI, and BFP. Recently, Hoseini et al. reported that high doses of vitamin D could significantly reduce BW, BMI, and visceral fat in rats with metabolic syndrome (37). In a trial study, Scragg et al. compared the serum levels of 25-OHD between obese subjects and non-obese controls and reported significantly lower levels in obese subjects (38). Vitamin D is a fat-soluble vitamin that is believed to store in larger adipose tissues after synthesizing and entering the bloodstream, releasing it at a slower rate. Vitamin D concentration in fat tissue is positively correlated with its serum concentration (39). Contrarily, hypovitaminosis D (a decrease in vitamin D) results in the increased levels of parathyroid hormone (PTH) and intercellular Ca⁺⁺ and inhibits insulin receptors in target tissues and closes the Glut-4 channel. In addition, since insulin secretion depends on the intracellular calcium concentration, hypovitaminosis D may impair insulin function, glucose metabolism, and other metabolic processes in the adipose tissue, which might be another mechanism in the association of abdominal obesity and low levels of vitamin D (37, 40). A further reduction in anthropometric indices induced by aerobic training plus vitamin D supplementation, compared to other groups, in the current study was probably due to the higher sensitivity of visceral adipocytes, which stimulated lipolysis in response to catecholamines. Moreover, aerobic training and vitamin D supplementation may have a direct effect on insulin sensitivity and beta cells function (14, 15). Since the increased BW, BMI, BFP, and WHR are risk factors for the development of insulin resistance, type 2 diabetes, and CVD in elderly women (8, 9), identifying the effective measures for reducing BMI, BFP, and WHR has always been a controversial issue. Further research is needed to document the vitamin D supplementation dose, training intensity, and cumulative effect of AT + Vit. D in improving anthropometric indices in NAFLD patients. The limitations of this study were the use of US to detect fatty liver, instead of liver biopsy as a more accurate technique, and the small sample size due to the limited number of patients with both vitamin D deficiency and NAFLD and their age-related limitations.