Vitamin D supplementation for improving sperm parameters in infertile men: A systematic review and meta-analysis of randomized clinical trials

Combination Therapy with Vitamin D and Metformin: A Potential Approach to Mitigate Testicular Dysfunction in Type 2 Diabetes Mellitus

Type 2 diabetes mellitus (T2DM) is a multifactorial disease that cannot be linked to a single pathway, causing the observed heterogeneity among T2DM patients. Despite this level of heterogeneity, T2DM is majorly managed by metformin (MET) monotherapy. However, recent findings have associated long-term metformin intake with progressive oxidative pancreatic β cell damage as the disease progresses. Hence, a significant number of patients treated with MET need an alternate therapy. Hence, identifying drug combinations that can effectively alleviate different diabetes complications would serve as a more promising therapy that can translate into active use. Hence, this study was designed to explore the possible synergistic effect of vitamin D and metformin on T2DM-induced testicular dysfunction. Thirty healthy male Wistar rats (weight: 120-150 g and age: 10 ± 2 weeks) were randomly divided into control, diabetes untreated (HFD+STZ), diabetes + vitamin D (1000 IU/kg), diabetes + metformin (180 mg/kg), and diabetes + vitamin D + metformin. All treatments lasted for 28 days and animals were sacrificed using IP injection of ketamine and xylaxine (40 and 4 mg/kg respectively). Vitamin D improved the ameliorative effect of metformin on T2DM-induced hyperglycemia and lipid dysmetabolism, accompanied by a significant decrease in testicular lactate dehydrogenase and lactate. Also, vitamin D + metformin significantly increased serum luteinizing hormone, follicle-stimulating hormone, testosterone, and testicular 5α reductase activities. Furthermore, vitamin D improved the anti-inflammatory and antioxidant effects of metformin by significantly decreasing T2DM-induced increase in testicular interleukin 1beta, interleukin 6, TNF-α, nitric oxide, and NF-κB and increasing T2DM-induced decrease in interleukin 10, glutathione, superoxide dismutase, catalase, GPx, and Nrf2. Vitamin D enhanced the ameliorative effect of metformin on T2DM-induced testicular dysfunction.

The Impact of Vitamin D on Androgens and Anabolic Steroids among Adult Males: A Meta-Analytic Review

BACKGROUND

Recent studies indicate that vitamin D impacts male reproductive function, with deficiency linked to infertility. This review evaluates the effect of vitamin D supplementation on male fertility, focusing on total testosterone, free testosterone, the free androgen index (FAI), follicle-stimulating hormone (FSH), luteinizing hormone (LH), sex-hormone-binding globulin (SHBG), and estradiol.

METHODS

We systematically searched Medline, Web of Science, Cochrane Library, and Scopus from their inception until July 2024 for randomized controlled trials (RCTs) involving adult males. The primary focus of these studies was on reproductive hormone parameters, analyzed using a random-effects meta-analysis and weighted mean difference (WMD). Evidence quality was assessed using ROB2 and GRADE. Meta-regression and dose-response analyses were performed.

RESULTS

Seventeen studies met the criteria for quantitative analysis. Vitamin D supplementation significantly increased total testosterone levels (WMD 0.38, 95% CI 0.06-0.70, n = 15, I2 = 67.03). However, it had no significant effect on other hormone parameters: free testosterone (WMD 0.00, 95% CI -0.02-0.03, n = 9, I2 = 48.12), FSH (WMD -0.02, 95% CI -0.57-0.53, n = 7, I2 = 48.72), LH (WMD -0.09, 95% CI -0.30-0.12, n = 8, I2 = 0.00), SHBG (WMD 0.73, 95% CI -1.14-2.61, n = 10, I2 = 69.05), FAI (WMD -0.92, 95% CI -2.12-0.27, n = 6, I2 = 0.00), and estradiol (WMD -0.02, 95% CI -2.95-2.92, n = 5, I2 = 20.63).

CONCLUSION

This meta-analysis shows that vitamin D supplementation may increase total testosterone levels in men. However, further well-designed RCTs are needed to determine vitamin D's effects on other reproductive hormone parameters.

Do Popular Diets Impact Fertility?

Infertility affects 15% of the population in developed countries, and its prevalence is increasing. Fertility can be influenced by different factors. Although key factors like maternal age cannot be changed, there is growing evidence that other modifiable factors, such as diet, can have an impact on fertility. Diet has become increasingly important in recent years for a number of reasons: the new trend toward a healthy lifestyle, the higher prevalence of certain digestive disorders, a lack of time that leads people to consume more prepared and processed food, and personal choice to not eat meat, among others. To meet these needs, several diets have recently become popular, such as the Mediterranean diet, known as the gold standard of health; the DASH diet, known for preventing hypertension; the Western diet, characterized by processed food; the ketogenic diet, characterized by low carbohydrate intake; and the vegetarian diet, which is the choice for people who do not eat meat or animal by-products. Diets present a unique composition characterized by the presence or absence of specific nutrients, which have also been associated with male and female fertility individually. This review assesses the impact of these diets and of macro- and micronutrients on both female and male fertility.

Effect of vitamin D metabolites and gene expression of vitamin D receptor, and 1-alpha-hydroxylase related to the sperm quality

The incidence of male fertility disorders has increased greatly due to various genetic and lifestyle factors. Recently, it has been hypothesized that vitamin D may be involved with idiopathic infertility. The goal of the study was to determine the effect and relationship between blood vitamin D metabolites, intracellular sperm vitamin D levels, and gene expression of 1-α-hydroxylase and VDR, with regard to semen quality. Seventy volunteers aged 25-45 were involved in the study. According to spermogram analysis, participants were stratified into normozoospermic control group, non-normozoospermic target group, and oligoasthenoteratozoospermic group. Vitamin D metabolites (total 25-hydroxycholecalciferol, 1,25-dihydroxycholecalciferol) in blood and spermatozoa were determined by ELISA. Free and bioavailable 25-hydroxycholecalciferol were calculated using the Vermeulen equation. mRNA expression of VDR and 1-α hydroxylase was evaluated by qPCR. Free and bioavailable 25-hydroxycholecalciferol were significantly higher in the control group compared to the target group and compared to the oligoasthenoteratozoospermic group . Intracellular sperm 1,25-dihydroxycholecalciferol was higher in the control group compared to the target group. The mRNA levels of 1- α-hydroxylase were significantly higher in the control samples, while VDR expression was significantly higher in the target group. Significant positive correlations were established between free and bioavailable 25-hydroxycholecalciferol with sperm motility and morphology. Vitamin D metabolites in blood and intracellular sperm 1,25-dihydroxycholecalciferol seem to exert beneficial effects on sperm motility and morphology. Regarding sperm quality, these effects are more pronounced in the free and bioavailable 25OHD compared to the total 25OHD in blood. Higher expression of 1-α-hydroxylase likely leads to higher intracellular levels of 1,25-dihydroxycholecalciferol, which could contribute to sperm motility and morphology. Higher VDR expression may be a compensatory mechanism related to lower intracellular sperm 1,25-dihydroxycholecalciferol.