Biochemical and dietary patterns of vitamin K and Magnesium pre-and post-sleeve surgery in morbidly obese Saudi males and females

1. Introduction

Obesity is a critical health problem in different corners of the globe. Recent evidence shows rising obesity rates in both developed and developing states (World Health Organization [WHO], 2020; World Obesity Federation, 2022). In Saudi Arabia, for example, approximately 40% of the population is either overweight or obese, with epidemiologists predicting this number to increase dramatically in the near future (Ministry of Health, 2018; Alsukait et al., 2022). Obesity is a critical health concern because it contributes to the severity of various health conditions, such as cognitive dysfunction, cancer, sleep apnea, infertility, and all-cause mortality (Phirom et al., 2025; Lauby-Secretan et al., 2016; Wang et al., 2020; Turner et al., 2025; Flegal et al., 2013). Therefore, the development of effective strategies to manage obesity is a crucial challenge for the public health system. Healthy diets and regular excercise have long been used to tackle this problem, but their implementation is often problematic due to the unwillingness or inability of patients to comply with strict restrictions and complete exercises on a regular basis. Moreover, the available evidence provides a compelling reason to believe that the long-term effectiveness of these measures is questionable. One recent study showed that patients regain approximately 80% of their lost weight within 5 years after the end of a weight loss program (Hall & Kahan, 2018). These limitations prevent many patients from managing their weight effectively.

Given these problems with traditional treatments, obese individuals across the globe are becoming increasingly interested in bariatric surgery (BS), especially sleeve gastrectomy (SG), which is its most popular type (English et al., 2018). The procedure involves removing a significant portion of a person’s stomach and is recommended to people whose body mass index (BMI) is above 40 kg/m² or above 35 kg/m², depending on whether they have obesity-related health problems (Hierons et al., 2022). Several meta-analysis studies showed the effectiveness of SG in causing substantial weight loss with fewer post-surgical complications than other weight loss surgical procedures (Han et al., 2020; Lei et al, 2024), making it one of the most popular obesity procedures globally.

Despite the popularity of SG, accumulating observations raise concerns about a possible decline in several trace elements such as vitamin K and magnesium (Mg) following the procedure (Pizzorno, 2016; Yu et al., 2014; Tian et al., 2020). Vitamin K regulates formation markers that contribute to bone formation and inhibits bone resorption, while Mg is an essential cofactor for healthy bone formation, among its other metabolic functions (Dominguez et al., 2025a; Dominguez et al., 2025b; Mederle et al., 2018). Therefore, possible deficits in vitamin K and Mg after SG can be a concerning issue that can inversely affect bone health. The existing knowledge of the link between SG and changes in vitamin K and Mg, however, is inconsistent, with different investigations reporting varied patterns (Pizzorno, 2016; Yu et al., 2014; Tian et al., 2020). Although risks of postoperative changes in vitamin K and Mg are recognized, the moderating role of the patient’s sex remains unclear. Evidence is limited on whether sex constitutes a non-modifiable risk factor for declines in these nutrients. To address this gap, the present study prospectively analyzed vitamin K and Mg levels as well as intakes in male and female patients undergoing SG.

2. Materials and Methods

2.1 Study design

This prospective study was conducted at King Fahad Medical City (KFMC) in Riyadh, Saudi Arabia, using an experimental research design. The study included 51 individuals, both males (n=19) and females (n=32). They had to meet a set of inclusion criteria based on their age (18-60 years), bone health (no previous history of bone disease), and BMI (>40 or >35 kg/m², depending on whether the patients had underlying comorbidities) (Fig. 1). The participants signed a consent form and underwent pre-surgery and post-surgery assessments. The study was approved by the Institutional Review Board (IRB) of the Department of Faculty of Medicine in King KFMC Research Center (IRB No. 21- 005).

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Fig. 1.

Flowchart of participants.

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3. Results

A total of 72 patients (32 males and 40 females) were deemed eligible for SG, 51 (19 males and 32 females) of whom had follow-up data. Table 1 shows the baseline characteristics and differences between male and female patients. Males had significantly higher weight, BMI, and WHR compared to females (p-values <0.001, <0.001, and 0.008). Baseline circulating vitamin K, MK-4, and MK-7, as well as Mg were not significantly different between males and females. However, baseline dietary vitamin K as well as dietary Mg were significantly higher in males than females (p-values 0.001 and <0.001). It is important to note that the dietary Mg was below RDA for all participants in all time points, while this was true for 90% of all participants (91% females and 89.5% males) for dietary vitamin K intake at baseline, reaching 100% in males and 94% in females after 12 months (not shown in Tables 1-4). Lastly, vitamin K deficiency [defined as serum vitamin K levels 0.21-3.07 ng/mL, (Nie et al., 2023)] was observed in 8 (16%) participants at baseline, decreasing to 5 (9.8%) after 12 months. (not shown in Tables 1-4).

Table 2 shows the post-surgery changes in anthropometrics, circulating and dietary vitamin K and Mg in all patients. As expected, significant reductions were seen in weight, BMI, and WHR over time in all follow-up visits. With regard to serum parameters of interest, no significant changes were seen in circulating vitamin K and MK-4 after 3 and 12 months of follow-up. However, a significant decrease was seen in circulating MK-7 after 3 months compared to baseline, with a modest but insignificant increase after 12 months of follow-up, which was still significantly lower than baseline. On the other hand, no differences were seen between baseline serum Mg and after 3 months, while a significant increase was observed after 12 months, which was significantly higher than values obtained at baseline and 3 months. Dietary changes in vitamin K and Mg were noted over time, with values after 3 months post-surgery observed to be drastically lower than baseline and having a slight recovery after 12 months, which was still significantly lower than baseline.

Over time, changes were also made after stratification according to sex. In males (Table 3), only serum Mg increased over time, while in females (Table 4), serum Mg also significantly increased with a concomitant decrease in serum MK-7 after 3 months (p=0.017). In both sexes, dietary changes followed the same patterns as the overall analysis, and there were significant reductions in dietary vitamin K and Mg after 3 months, with a modest recovery after 12 months (Tables 3 and 4).

In all participants, Fig. 2 showed a significant positive correlation between dietary Mg and dietary vitamin K (r=0.47; p<0.001) as well as over time changes between circulating MK4 and vitamin K (r=0.46; p<0.001) (Fig. 3).

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Fig. 2.

Correlation between baseline dietary vitamin K and Mg for all subjects.

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Fig. 3.

Correlation between overtime changes in serum MK4 and vitamin K in all subjects.

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4. Discussion

It is known that several vulnerable populations, such as pregnant women and individuals with obesity, have marked vitamin and trace mineral deficiencies prior to undergoing BS (Bradley et al., 2023; Bretón et al., 2024). Among these micronutrients previously investigated, however, Mg and vitamin K remain understudied. In the present study, we aimed to determine prospective changes in circulating Mg and vitamin K among males and females who underwent laparoscopic SG and found that post-operation, and in all participants, no notable changes were seen in serum levels of vitamin K over time, while serum Mg showed recovery 12 months after surgery. When stratified according to sex, the same patterns were observed in both trace elements. These changes were parallel to the expected weight loss over time. Consequently, while dietary intakes of vitamin K and Mg improved in both males and females 12 months as compared to 3 months post-surgery, this favorable increase was still lower compared to baseline dietary values, the majority, if not all, of whom were already below RDA prior to surgery.

A recent systematic review involving 19 studies, 12 of which had data after BS (n=1442), indicated that while individuals who undergo such procedures were at higher risk for developing vitamin K deficiency, the strength of evidence was weak and therefore supplementation was not recommended (Sherf-Dagan et al., 2019). Similarly, vitamin K deficiency in the presented study decreased over time, albeit not significant, suggesting that the procedure did not alter the incidence of vitamin K deficiency. As for changes in circulating Mg, evidence is inconsistent. In a recent comparative study that assessed nutritional deficiencies among individuals who underwent Roux-en-Y gastric bypass (n=340) versus SG (n=165), Mg deficiency (which ranged from 24%-31%) remained prevalent in both groups with no apparent significant changes seen even after 12 months of follow-up (Vieira de Sousa et al., 2024). Other, less recent studies, however, support the present study’s findings, which demonstrated improved Mg levels over time following surgery (Haenni et al., 2018), and even moderate weight loss among individuals with obesity (Mikalsen et al., 2019). These differences in findings can be attributed to the type of surgery performed and whether the patients were provided with supplementation before the procedure.

One of the novel findings of the present study is the sexual dimorphism observed in vitamin K homologs, specifically MK7, the active form of vitamin K, which was seen to substantially decrease in females, but not in males, despite having relatively similar vitamin K levels over time. MK7 (or vitamin K2) is known to have the highest bioavailability and exerts the greatest effect on osteocalcin carboxylation in humans, suggesting that its main role is associated with bone health and quality (Sato et al., 2020). The decreased MK7 observed only in females may partially explain the increased risk for low bone mineral density and osteoporosis following BS (Ou et al., 2022). This is most apparent in a recent clinical trial, where declining estrogen during menopause accelerated bone loss, while MK-7 supplementation supported bone and cardiovascular health by activating vitamin-K-dependent proteins (de Vries et al., 2025). Furthermore, vitamin K is primarily known as a cofactor for blood coagulation, mechanisms of which are partially driven by sex hormones, which explains the female-specific hypercoagulability (Coleman et al., 2024). Given that MK7 decreased over time only in females, the protective hypercoagulability effect that confers better outcomes than males following injury suggests that this advantage may be lost after SG. More studies are needed to confirm this theory.

Lastly, it is important to mention that all participants failed to meet the RDA for dietary Mg, and most of them for dietary vitamin K, reinforcing the prevalent dietary micronutrient deficiencies among BS candidates (Bradley et al., 2023). This is important as many physicians fail to actively screen patients for micronutrient deficiencies. In a recent survey conducted among 160 patients who underwent BS in Saudi Arabia, although micronutrient deficiencies were assessed through blood exams as well as provision of dietary guidance, dietary intake was unfortunately not taken, concluding that pre- and post-surgery nutrients need closer monitoring (Qadhi et al., 2023).

The authors acknowledge several limitations. The lack of a comparator group that underwent the same surgery but was not given multivitamins limited the findings as to the true changes in serum Mg and vitamin K after surgery. This, however, is difficult as pre-operative management requires that all patients be given multivitamin supplementation aside from dietary advice. The small sample size after stratification for sex may have elicited several type 2 errors in analysis, giving non-significant differences that may otherwise not be. Lastly, major micronutrients such as iron, vitamin D, and other well-studied trace elements were not assessed, given that they have been well investigated, albeit not in a similar population. Despite the caveats, findings of the study are robust and complement existing literature on the effects of SG on key micronutrients, vitamin K, and Mg in particular. The inclusion of vitamin K homologs also adds value to the study as well as the use of heterogenous Arab patients. Further studies with longer follow-up and larger sample sizes are needed to determine whether such deficiencies persist.

5. Conclusions

In conclusion, parallel to a significant weight loss, a substantial but modest recovery in circulating and Mg, while no apparent changes in vitamin K were observed among Arab patients one year after SG. MK7 levels were seen to decrease over time only in females. Dietary Mg and vitamin K intakes were below RDA in almost all patients. Longer studies are needed to determine whether these micronutrient deficiencies remain and whether the changes observed in vitamin K homologs are associated with SG-related complications.