In the current investigation, subsequent to conducting Backward stepwise regression analysis, the variables of age, gender, BMI, smoking, and two supplements comprising ferric compounds and folic acid persisted in the model. Between these two supplements, solely ferric compounds exhibited a significant association with abdominal obesity and was acknowledged as a protective factor, leading to a 27% lower likelihood of abdominal obesity in individuals who consumed ferric compounds compared to those who did not utilize this supplement.

The findings of the studies demonstrated that ferric compounds deficiency anemia can result in fatigue and further exacerbate weight gain by diminishing physical activity³⁰. Additionally, observations from mouse model investigations revealed that ferric compounds supplementation reduces weight gain induced by diet and intrahepatic fat accumulation. It appears that ferric compounds supplementation mitigates the morphological irregularities of mitochondria in skeletal muscle and enhances the expression of genes linked to the mitochondrial electron transport chain and energy metabolism in skeletal muscle and liver³¹. Consequently, it is plausible that ferric compounds supplementation can yield a favorable impact on reducing abdominal circumference and ameliorating central obesity.

In the present study, the association between calcium supplementation and abdominal obesity was found to be insignificant. Earlier research has indicated an inverse correlation between calcium intake through diet and abdominal obesity, indicating that a decrease in calcium intake is associated with an increase in abdominal fat³². Conversely, an increase in calcium intake through diet diminishes the risk of abdominal obesity²². Furthermore, the outcomes of a meta-analysis revealed that the consumption of low-fat dairy products, as part of a diet with restricted energy intake, contributes to body fat loss over a period of 4 months, whereas calcium supplements do not yield the same effect³³.

Contrary to expectations, the results of studies pertaining to supplemental calcium present a different picture. According to the obtained results, calcium obtained through supplements rather than through diet has minimal or no impact on weight or body composition³³. For instance, the study conducted by Huang et al. on 8940 adults aged 20 to 74 demonstrated that while dietary calcium is associated with a decrease in abdominal obesity in women, supplemental calcium consumption has no relationship with abdominal obesity and body composition in either the male or female groups²².

The proposition has been put forward that dairy sources of calcium have a notable impact on weight and fat gain reduction, as well as an acceleration of fat loss, to a greater extent than calcium supplements. This augmented effect of dairy products relative to supplemental calcium is likely attributed to additional bioactive compounds, such as angiotensin-converting enzyme inhibitors, and the abundant concentration of branched-chain amino acids, which work synergistically with calcium to diminish obesity³⁴.

Within present investigation, no significant association between vitamin D supplementation and abdominal obesity was discovered. As documented in certain sections of the literature, vitamin D supplementation does not exert a substantial influence on abdominal obesity. Specifically, a meta-analysis conducted in 2020 encompassing 11 clinical trials exploring the association between vitamin D and abdominal obesity indicated that vitamin D did not significantly decrease waist circumference when compared to a placebo³⁵. Furthermore, another meta-analysis conducted in 2023 concerning the association between vitamin D and abdominal obesity in patients with metabolic syndrome concluded that vitamin D supplementation induced a significant reduction in waist circumference in only one out of five studies. The researchers conducting the study emphasized that the low certainty of evidence did not support the hypothesis of waist circumference reduction due to vitamin D supplementation³⁶. Nevertheless, apart from these studies, a meta-analysis concluded that there was an inverse relationship between vitamin D blood levels and abdominal circumference, whereby every 25 nmol/liter increase in vitamin D levels increased the risk of abdominal obesity by 10%³⁷. Most of the active vitamin D is supplied in the body via exposure to sunlight, while the contribution from dietary intake is negligible. However, supplements can alleviate vitamin D deficiency. Research findings indicate that the bioavailability of various types of vitamin D supplements differs, resulting in varying levels of vitamin D in the blood³⁸. However, once vitamin D enters the bloodstream and attains an optimal level, it can mitigate the risk of abdominal obesity³⁷. Thus, one possible explanation for the lack of association between vitamin D supplement usage and abdominal obesity in some parts of the research like the current study may be the failure to attain the optimal blood level of vitamin D.

In the present study, there was no correlation between omega-3 consumption and abdominal obesity. However, a meta-analysis of 11 RCTs (updated to 2015) concluded that omega-3 PUFA may effectively reduce waist circumference and triglyceride levels in overweight and obese adults, although it may not effectively reduce body weight. Of course, it was emphasized in this study that due to the small number and poor quality of RCTs in the meta-analysis, the results obtained were not definitive³⁹. In addition, in a clinical trial study that was conducted in 2017 to determine the effect of omega-3 on weight reduction in obese people on a weight loss diet, two groups including the weight loss diet group and the weight loss diet group plus omega 3 were included²¹. In this study, a significant decrease in weight, waist circumference, and BMI was observed in both groups, but the mass and percentage of abdominal fat in the omega-3 group decreased significantly more than the control group. According to the findings of this study, omega-3 PUFA supplementation decreased the mass and percentage of abdominal fat in overweight or obese people on a weight loss diet. Therefore, it can be concluded that omega-3 consumption can play an effective role in reducing abdominal circumference. The bottom line, what draws attention in these studies is that the dose of omega-3 used in the mentioned studies was between 1.2 and 5 g per day⁴⁰. The reason for this could be that in Iran, during the time of the study, the omega-3 products were primarily consumed with the intention of prevention, resulting in a dosage of less than 1000 mg per day. Hence, it appears that one of the rationales for the absence of mentioned association in the current investigation may be the substantially lower dosage administered to the study participants compared to the dosage employed in the aforementioned studies.

In this investigation, folic acid exhibited a noteworthy association with abdominal obesity in the univariable logistic regression analysis; however, this association failed to retain its significance in the multivariable analysis. The investigation of folic acid’s role as a supplement in abdominal obesity has been conducted in animal and human studies, resulting in conflicting findings. For example, a 2016 study on mice by Kelly et al. demonstrated that consuming a high-fat diet with extra folic acid may cause weight gain, heightened fat mass, adipose tissue inflammation, and systemic glucose intolerance⁴¹. However, a case-control study was carried out by Mlodzik-Czyzewska et al. in 2020, focusing on healthy, obese, and non-obese individuals, revealed an association between a reduced intake of folate and its low serum levels with both higher body mass index and increased fat accumulation in the abdominal region⁴². Moreover, a systematic review-meta-analysis conducted in 2018 demonstrated no correlation between blood folate levels and body mass index among individuals⁴³. Given the contradicting findings concerning folate intake and its serum levels, and abdominal obesity, it is imperative to conduct further investigations in this particular field.

In current research, we defined abdominal obesity using waist circumference cutoffs of 102 cm for men and 88 cm for women, which are commonly applied in clinical and research settings. However, alternative cutoffs exist depending on specific population characteristics, such as ethnicity and health risk profiles. Using a lower cutoff would likely increase the prevalence of abdominal obesity in our sample, potentially strengthening the observed associations with supplement use, whereas higher thresholds might reduce the prevalence and weaken these associations. Since the relationships identified in this study could be influenced by the choice of cutoff values, selecting a more common standard definition might guarantee comparability across studies.

This study provides a unique contribution to the literature by highlighting a specific association between the use of ferric compounds and a reduced risk of abdominal obesity. While previous research has largely focused on the general health benefits of iron⁴⁴, few studies have explored the role of iron supplementation in reducing central adiposity specifically. Our findings suggest a potential protective effect of ferric compounds on abdominal obesity, which could be a novel area for further investigation and may differentiate this study from others in the field. Moreover, this research is the first large-scale investigation within an Iranian population to examine the relationship between dietary supplement use and abdominal obesity. Given the specific dietary habits and genetic factors of this population, our study not only adds to the understanding of these associations within Iran but also provides a foundation for comparative studies in other populations.

The findings of this study highlight the role of dietary supplements, particularly ferric compounds, in abdominal obesity. However, abdominal obesity is influenced by a multifaceted interplay of demographic, behavioral, and biological factors. Our results suggest that supplement use may interact with variables such as gender, BMI, and some other lifestyle factors, potentially modifying their impact on abdominal obesity. For instance, the observed gender differences in supplement consumption patterns could reflect underlying disparities in health behaviors or metabolic responses. Similarly, the relationship between BMI and abdominal obesity might be further modulated by the type and frequency of supplement use. Future studies are needed to explore these complex interactions and their implications for public health interventions.

Implications for practice and future research

The findings from this study suggest that dietary supplements, particularly ferric compounds, may have implications for managing abdominal obesity. In clinical practice, healthcare providers might consider the potential role of ferric supplementation as part of a broader nutritional and lifestyle intervention strategy for individuals at risk of abdominal obesity. However, these results should be interpreted with caution, as they are based on a cross-sectional study. Therefore, longitudinal studies are needed to establish causal relationships. Future research should focus on exploring the underlying biological mechanisms that may link ferric compounds with central adiposity, such as their effects on inflammation and lipid metabolism. Additionally, it would be valuable to investigate whether similar patterns are observed in different populations with varying dietary and genetic backgrounds to assess the generalizability of these findings. Further randomized controlled trials examining the effects of iron and other specific supplements on abdominal obesity could provide more robust evidence for clinical guidelines and recommendations.

Strengths and limitations

The current study was conducted on the data derived from a large comprehensive population of Iranian 35–70 year‒adults using valid instruments and professional interviewers. Despite these strengths, there were some limitations in our investigation. At first, this study utilized a cross-sectional design, which inherently limits the ability to establish causal relationships between supplement consumption and abdominal obesity. While our findings provide valuable insights into potential associations, they should be interpreted with caution. Longitudinal studies are required to confirm causality and further investigate the temporal dynamics of these relationships. Second, in this study, waist circumference was used as the sole measure of abdominal obesity, with cutoff values based on international standards. These thresholds were selected to facilitate comparisons of our findings with studies conducted in other countries. However, using non-Iranian cutoff values may not fully reflect the specific anthropometric characteristics of the Iranian population, which could impact the accuracy of obesity classification. Third, the complete and accurate data on dosage and duration and also being present or past users of the supplements was not accessible for the researchers. Forth, the exact contents of some supplements such as multivitamins were not specified. Fifth, despite the large sample size, the participants in this study were not representative of the entire population of Iran because this population belongs to a limited region within one of the cities located in Yazd province, which is one of the thirty-one provinces of Iran.