The effect of vitamin A supplementation on thyroid function in premenopausal women

Effects of primary or secondary prevention with vitamin A supplementation on clinically important outcomes: a systematic review of randomised clinical trials with meta-analysis and trial sequential analysis

OBJECTIVES

This systematic review with meta-analyses of randomised trials evaluated the preventive effects of vitamin A supplements versus placebo or no intervention on clinically important outcomes, in people of any age.

METHODS

We searched different electronic databases and other resources for randomised clinical trials that had compared vitamin A supplements versus placebo or no intervention (last search 16 April 2024). We used Cochrane methodology. We used the random-effects model to calculate risk ratios (RRs), with 95% CIs. We analysed individually and cluster randomised trials separately. Our primary outcomes were mortality, adverse events and quality of life. We assessed risks of bias in the trials and used Grading of Recommendations, Assessment, Development, and Evaluations (GRADE) to assess the certainty of the evidence.

RESULTS

We included 120 randomised trials (1 671 672 participants); 105 trials allocated individuals and 15 allocated clusters. 92 trials included children (78 individually; 14 cluster randomised) and 28 adults (27 individually; 1 cluster randomised). 14/105 individually randomised trials (13%) and none of the cluster randomised trials were at overall low risk of bias. Vitamin A did not reduce mortality in individually randomised trials (RR 0.99, 95% CI 0.93 to 1.05; I²=32%; p=0.19; 105 trials; moderate certainty), and this effect was not affected by the risk of bias. In individually randomised trials, vitamin A had no effect on mortality in children (RR 0.96, 95% CI 0.88 to 1.04; I²=24%; p=0.28; 78 trials, 178 094 participants) nor in adults (RR 1.04, 95% CI 0.97 to 1.13; I²=24%; p=0.27; 27 trials, 61 880 participants). Vitamin A reduced mortality in the cluster randomised trials (0.84, 95% CI 0.76 to 0.93; I²=66%; p=0.0008; 15 trials, 14 in children and 1 in adults; 364 343 participants; very low certainty). No trial reported serious adverse events or quality of life. Vitamin A slightly increased bulging fontanelle of neonates and infants. We are uncertain whether vitamin A influences blindness under the conditions examined.

CONCLUSIONS

Based on moderate certainty of evidence, vitamin A had no effect on mortality in the individually randomised trials. Very low certainty evidence obtained from cluster randomised trials suggested a beneficial effect of vitamin A on mortality. If preventive vitamin A programmes are to be continued, supporting evidence should come from randomised trials allocating individuals and assessing patient-meaningful outcomes.

PROSPERO REGISTRATION NUMBER

CRD42018104347.

Is beta-carotene consumption associated with thyroid hormone levels?

The thyroid hormones play a pivotal role in various physiological processes, including growth, metabolism regulation, and reproduction. While non-modifiable factors are known to impact thyroid function, such as genetics and age, nutritional factors are also important. Diets rich in selenium and iodine are conventionally acknowledged to be beneficial for the production and release of thyroid hormones. Recent studies have suggested a potential link between beta-carotene, a precursor to vitamin A (retinol), and thyroid function. Beta-carotene is known for its antioxidant properties and has been shown to play a role in the prevention of various clinical conditions such as cancer and cardiovascular and neurological diseases. However, its impact on thyroid function is still unclear. Some studies have suggested a positive association between beta-carotene levels and thyroid function, while others have found no significant effect. Conversely, the hormone produced by the thyroid gland, thyroxine, enhances the conversion of beta-carotene to retinol. Furthermore, vitamin A derivatives are being explored as potential therapeutic options for thyroid malignancies. In this review, we highlight the mechanisms through which beta-carotene/retinol and thyroid hormones interact and review the findings of clinical studies examining the association between beta-carotene consumption and thyroid hormone levels. Our review underscores the need for further research to clarify the relationship between beta-carotene and thyroid function.

The impact of vitamin A supplementation on thyroid function and insulin sensitivity: implication of deiodinases and phosphoenolpyruvate carboxykinase in male Wistar rats

Purpose

Vitamin A is an essential nutrient with vital biological functions. The present study investigated the effect of different doses of vitamin A palmitate at different time intervals on thyroid hormones and glycemic markers.

Methods

Male rats were administrated vitamin A palmitate at different doses (0, 0.7, 1.5, 3, 6, and 12 mg/kg, oral) and samples were collected at different time intervals of 2, 4, and 6 weeks. The levels of vitamin A, thyroid hormones (T3, T4, and TSH), deiodinases (Dio1 and Dio3), glycemic markers (blood insulin and fasting glucose levels, HOMA IR and HOMA β), retinol-binding protein 4 (RBP4) and the gluconeogenic enzyme phosphoenolpyruvate carboxykinase (PEPCK) were measured.

Results

The findings demonstrated that long-term supplementation with high doses of vitamin A palmitate resulted in hypothyroidism (lower T3 and T4 levels and elevated TSH levels) as well as upregulation of Dio1 and Dio3 expression levels. This effect was associated with elevated glucose and insulin levels, enhanced HOMA IR, and decreased HOMA B index. In addition, prolonged vitamin A supplementation significantly increased RBP4 levels that upregulated the expression of PEPCK.

Conclusion

High doses of vitamin A supplementation increased the risk of hypothyroidism, modulated insulin sensitivity, and over a long period, increased the incidence of type 2 diabetes mellitus associated with oxidative stress and hepatitis.

The relationship between thyroid disorders and vitamin A.: A narrative minireview

The terms "vitamin A" and "retinoids" encompass a group of fat-soluble compounds essential for human nutrition. Some of them (retinol, retinal, 9-cis-retinoic acid, tretinoin, and 13-cis-retinoic acid) are fully natural, while others are synthetic compounds used mostly for therapeutic purposes. Some evidence indicates that the nutritional status of these retinoids (i.e., the presence or absence of deficiency) is able to modulate thyroid gland metabolism. Vitamin A deficiency is tightly correlated with structural and functional impairment of the thyroid gland and is often associated with iodine deficiency. Furthermore, retinoids are involved in different immune functions, as well as in the process of activation, proliferation, and differentiation of regulatory T cells (Treg). This is particularly significant given the high prevalence of thyroid autoimmune disorders, whose pathogenesis seems to be related to the altered homeostasis of regulatory T cells. Retinoids are also involved in the modulation of gene expression via their interaction with nuclear receptors, and they also act as cofactors in cell growth and differentiation. The ability of retinoic acid to increase iodine uptake and sodium-iodine symporter activity in human thyroid cancer cell lines suggests that some retinoids and their derivatives may be of use in the treatment of different thyroid tumors. This minireview summarizes the current knowledge on the link between nutritional intake of vitamin A and various thyroid disorders.

Randomized Study of the Effects of Zinc, Vitamin A, and Magnesium Co-supplementation on Thyroid Function, Oxidative Stress, and hs-CRP in Patients with Hypothyroidism

Hypothyroidism can occur due to deficiencies in micronutrients such as zinc, magnesium, and vitamin A. The aim of this study was to determine the effects of supplementation with these micronutrients on thyroid function, oxidative stress, and hs-CRP levels in patients with hypothyroidism. In a randomized double-blind, placebo-controlled trial with two parallel groups, 86 hypothyroid patients aged 20-65 were allocated to receive daily supplementation with either: (intervention group, n = 43) one 30 mg zinc gluconate capsule per day, one 250 mg magnesium oxide tablet per day, and one 25,000 IU vitamin A capsule twice/week for 10 weeks or (placebo group, n = 43) placebo capsules and tablets as above for 10 weeks. Neither of the groups changed their diet or physical activity. Thyroid hormones (free and total thyroxine (FT4 and TT4), free tri-iodothyronine (FT3), and thyroid-stimulating hormone (TSH)), oxidative markers (malondialdehyde (MDA) and total antioxidant capacity (TAC)), serum hs-CRP, and anthropometric indices (height and weight) were assessed at the baseline and at the end of the study. In the intervention group, we found a significant increase in serum FT4, decreased anthropometric indices, and lower levels of serum hs-CRP by the end of the 10 week protocol (P < 0.05). In the placebo group, serum TAC was decreased and hs-CRP increased (P < 0.05), with no significant changes in serum TSH, FT3, TT4, and MDA after the intervention. Zinc, vitamin A, and magnesium supplementation may have beneficial effects in patients with hypothyroidism and in diseases associated with hyperthyroidism.

Effect of Micronutrients on Thyroid Parameters

Micronutrients are involved in various vital cellular metabolic processes including thyroid hormone metabolism. This study aimed to investigate the correlation between serum levels of micronutrients and their effects on thyroid parameters. The correlation of serum levels of micronutrients and thyroid markers was studied in a group of 387 healthy individuals tested for thyroid markers (T4, T3, FT4, FT3, TSH, anti-TPO, RT3, and anti-Tg) and their micronutrient profile at Vibrant America Clinical Laboratory. The subjects were rationalized into three groups (deficient, normal, or excess levels of micronutrients), and the levels of their thyroid markers were compared. According to our results, deficiency of vitamin B2, B12, B9 and Vit-D25[OH] ( $p<0.05$ ) significantly affected thyroid functioning. Other elemental micronutrients such as calcium, copper, choline, iron, and zinc ( $p<0.05$ ) have a significant correlation with serum levels of free T3. Amino acids asparagine (r = 0.1765, $p<0.001$ ) and serine (r = 0.1186, $p<0.05$ ) were found to have a strong positive correlation with TSH. Valine, leucine, and arginine ( $p<0.05$ ) also exhibited a significant positive correlation with serum levels of T4 and FT4. No other significant correlations were observed with other micronutrients. Our study suggests strong evidence for the association of the levels of micronutrients with thyroid markers with a special note on the effect of serum levels of certain amino acids.

Metribuzin-induced non-adverse liver changes result in rodent-specific non-adverse thyroid effects via uridine 5'-diphospho-glucuronosyltransferase (UDPGT, UGT) modulation

Metribuzin is a herbicide that inhibits photosynthesis and has been used for over 40 years. Its main target organ is the liver and to some extent the kidney in rats, dogs, and rabbits. Metribuzin shows a specific thyroxine (T4) profile in rat studies with T4 increases at low doses and T4 decreases at higher doses. Only the T4 decreases occur together with histopathological changes in the thyroid and weight changes of liver and thyroid. A set of experiments was conducted to investigate metribuzin's endocrine disruptor potential according to European guidance and regulations. The results indicate that a liver enzyme modulation, i.e. of the uridine 5'-diphospho-glucuronosyltransferase (UDPGT, UGT), is most likely responsible for both increased and decreased plasma thyroxine level and for thyroid histopathological observations. Animals with high T4 levels show low UGT activity, while animals with low T4 levels show high UGT activity. A causal relationship was inferred, since other potentially human-relevant mode of action (MOA) pathways were excluded in dedicated studies, i.e. inhibition of deiodinases (DIO), inhibition of thyroid peroxidase (TPO) or of the sodium importer system (NIS). This liver metabolism-associated MOA is considered not relevant for human hazard assessment, due to species differences in thyroid homeostasis between humans and rats and, more importantly, based on experimental data showing that metribuzin affects UGT activity in rat but not in human hepatocytes. Further, we discuss whether or not increased T4 levels in the rat, in the absence of histopathological changes, should be considered as adverse and therefore used as an appropriate hazard model for humans. Based on a weight of evidence approach, metribuzin should not be classified as an endocrine disruptor with regard to the thyroid modality.

The effects of powdered black cumin seeds on markers of oxidative stress, intracellular adhesion molecule (ICAM)-1 and vascular cell adhesion molecule (VCAM)-1 in patients with Hashimoto's thyroiditis

OBJECTIVE

Oxidative stress plays an important role in the pathogenesis of Hashimoto's thyroiditis. Because of the major anti-oxidant properties of black cumin, the current study aimed to evaluate the effect of powdered Nigella sativa seeds on markers of oxidative stress, endothelial dysfunction and serum lipids in patients with Hashimoto's thyroiditis.

METHODS

Forty patients with Hashimoto's thyroiditis, aged between 22 and 50 years old, participated in the trial and were randomly allocated into two groups of intervention and control receiving powdered N. sativa or placebo daily for 8 weeks. Changes in markers of oxidative stress, including total anti-oxidant capacity (TAC), malondialdehyde (MDA), superoxide dismutase (SOD), glutathione peroxidase (GPX), and biomarkers of endothelial dysfunction including Intracellular Adhesion Molecule (ICAM)-1, Vascular Cell Adhesion Molecule (VCAM)-1 and serum lipids were also evaluated.

RESULTS

Treatment with N. sativa, significantly increased serum TAC, SOD and reduced MDA concentrations with no significant change in GPX (P < 0.05). A significant reduction in VCAM-1 (P = 0.0012), body mass index (P = 0.002), serum concentrations of low density lipoprotein cholesterol (P = 0.002) and triglyceride (P = 0.02) were also reported in N. sativa-treated group after 8 weeks; while serum high density lipoprotein cholesterol (HDL) also significantly increased (P < 0.05). No change in other parameters were reported.

CONCLUSIONS

Giving attention to the potent beneficial effects of powdered black cumin seeds in improving oxidative stress, endothelial dysfunction, serum lipids and anthropometric features in patients with Hashimoto's thyroiditis, this medicinal plant can be considered as a therapeutic agent in management of Hashimoto-related metabolic abnormalities.

TRIAL REGISTRATION NUMBER

Iranian registry of clinical trials (registration number IRCT2015021719082N4).

Micronutrients, iodine status and concentrations of thyroid hormones: a systematic review

Context

The metabolism of thyroid hormones, which are essential for normal development, involves many proteins and enzymes. It requires iodine as a key component but is also influenced by several other micronutrients, including selenium, zinc, iron, and vitamin A.

Objective

This systematic review was designed to investigate the effect of micronutrient status and supplementation on iodine status and thyroid hormone concentrations.

Data Sources

Using the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analysis) guidelines, electronic databases were searched from their inception to April 2016.

Study Selection

Human studies published in English and reporting data on micronutrient status and iodine status and/or thyroid hormone concentrations were included. Studies that examined the effect of micronutrient supplementation on iodine status and/or thyroid hormone concentrations were also included.

Data Extraction

A predesigned and piloted data extraction form was used to compile data from individual studies.

Results

A total of 57 studies were included: 20 intervention studies and 37 observational studies. Although observational evidence suggests that concentrations of selenium, zinc, and iron are positively associated with iodine status, data from randomized controlled trials fail to confirm this relationship.

Conclusions

Further studies are needed to provide greater understanding of the role of micronutrient status in iodine nutrition and thyroid function to ascertain the public health implications for populations worldwide.

Effects of selenium and vitamin C on the serum level of antithyroid peroxidase antibody in patients with autoimmune thyroiditis

PURPOSE

Selenium (Se), an essential trace element, has been implicated in pathogenesis of autoimmune thyroiditis (AIT). Most studies attributed the immune modulating effects of Se to its antioxidant properties. However, there is insufficient evidence to support the use of selenium supplementation or other antioxidants in patients with AIT. This clinical trial was designed to investigate the impact of Se and vitamin C supplementation on antithyroid peroxidase antibody (TPO-Ab) level in patients with AIT.

METHODS

One hundred and two subjects aged 15-78 years were randomized into three groups. Group one (GI) (n = 38) was treated with 200 μg/day sodium selenite, group two (GII) (n = 36) received 500 mg vitamin C/day, and group three (GIII) (n = 28) received placebo over a 3-month period. Thyroid stimulating hormone (TSH), TPO-Ab, antithyroglobulin antibody (Tg-Ab) and Se concentrations were once measured before treatment and at the end of the study.

RESULTS

After 3 months, TPO-Ab concentrations decreased within Se and vitamin C-treated groups, but did not change in the placebo subjects. In this regard, there was no significant difference between the groups. We also did not find any statistically significant difference in TSH and Tg-Ab levels within and between the groups. At the end of the study, Se level was significantly higher in GI compared with GII and GIII.

CONCLUSION

Our findings supported the hypothesis of antioxidant beneficial effects of Se in AIT. However, it was not superior to vitamin C, regarding its effects on thyroid-specific antibodies.

Powdered black cumin seeds strongly improves serum lipids, atherogenic index of plasma and modulates anthropometric features in patients with Hashimoto's thyroiditis

Background

Hashimoto’s thyroiditis is associated with serious alterations in serum lipids and glucose homeostasis. The aims of the current study were to evaluate the effect of powdered Nigella sativa on serum lipids, glucose homeostasis and anthropometric variables in patients with Hashimoto’s thyroiditis.

Methods

Forty patients with Hashimoto’s thyroiditis, aged between 22 and 50 years old, participated in the trial and were randomly allocated into two groups of intervention and control receiving powdered Nigella sativa or placebo daily for 8 weeks. Serum lipids, glucose homeostasis, and anthropometric variables were evaluated at baseline and after intervention.

Results

Treatment with Nigella sativa significantly reduced body weight and body mass index (BMI). Serum concentrations of low density lipoprotein cholesterol (LDL) and triglyceride (TG) also decreased in Nigella sativa-treated group after 8 weeks; while serum high density lipoprotein cholesterol (HDL) significantly increased after treatment with Nigella sativa (P < 0.05). None of these changes had been observed in placebo treated group. Serum Nesfatin-1 concentrations was in inverse relationship with serum triglyceride (TG) (r = − 0.31, P = 0.04).

Conclusions

Giving attention to the potent beneficial effects of powdered black cumin seeds in improving serum lipid profile and anthropometric features in patients with Hashimoto’s thyroiditis, this medicinal plant could be considered as a beneficial herbal supplement alongside with the disease- specific medications including Levothyroxine in management of Hashimoto’s thyroiditis- related metabolic abnormalities.

Trial registration

Iranian registry of clinical trials (registration number IRCT2014090819082N2- Registered 2014-09-29).

Vitamin A supplementation reduces the Th17-Treg - Related cytokines in obese and non-obese women

OBJECTIVE

The objective of the present study was to investigate the effect of vitamin A supplementation on serum Th17 (IL-6, IL-17, IFNγ) and Treg (TGF-β, IL-10) related cytokines in obese and non-obese women.

SUBJECTS AND METHODS

In a randomized double blind placebo controlled design, 56 obese women were randomly assigned to receive either an oral dose of 25,000 IU retinyl palmitate or placebo per day for 4 months. Twenty eight ages matched non-obese women were also received vitamin A. At the study entry, anthropometric variables were measured and serum Th17 and Treg related cytokine profile were determined at baseline and 4 months after intervention.

RESULTS

Significantly higher baseline concentrations of IL-6 were observed in obese compared with non-obese women (P < 0.05). However, the initial concentrations of other cytokines were not significantly different between groups. The mean concentrations of IL-17 and TGF-β were significantly decreased after vitamin A supplementation in non-obese and obese women respectively. Positive relationships between IL-17 and IL-10 (r = 0.42, P < 0.001), TGF-β and IL-17 (r = 0.35, P < 0.001) and between IL-10 and IFN-γ (r = 0.41, P = 0.002) in total participants were also observed.

CONCLUSIONS

The results of the present study showed for the first time that vitamin A supplementation reduces serum concentrations of IL-17 and TGF-β in reproductive age women. Further studies are needed to explore the possible underlying mechanisms.

The effect of enriched chicory inulin on liver enzymes, calcium homeostasis and hematological parameters in patients with type 2 diabetes mellitus: A randomized placebo-controlled trial

BACKGROUNDS AND AIMS

Type 2 diabetic mellitus (T2DM) as one of the main causes of morbidity and mortality is associated with immune system disturbances and metabolic abnormalities. In the current study we aimed to evaluate the effects of enriched chicory inulin supplementation on liver enzymes, serum calcium and phosphorous concentrations and hematological parameters in patients with T2DM.

METHODS

Forty-six diabetic females patients were randomly allocated into intervention (n=27) and control (n=22) groups. Subjects in the intervention group received a daily dose of 10g of chicory and subjects in control group received a placebo for two months. Anthropometric variables, glucose homeostasis, hematological parameters and metabolic indices including serum alanine aminotransfersae (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), calcium and phosphorous as well as creatinine concentrations, glomerular filtration rate (GFR) and blood pressure were assessed at the beginning and end of the trial.

RESULTS

Significant reductions in fasting serum glucose (FSG), Hb A1C, AST and ALP concentrations were observed in chicory-treated group. Systolic and diastolic blood pressures were also reduced in chicory-treated group. Serum calcium significantly increased after chicory supplementation but no change in placebo treated group has been occurred (P=0.014). Supplementation with enriched chicory for two months significantly reduced hematocrit and mean corpuscular volume (MCV) values (P<0.05). Changes in serum insulin, creatinine and GFR were not significant.

CONCLUSION

The present study showed beneficial effects of oligofructose-enriched chicory on the improvement of the glucose and calcium homeostasis, liver function tests, blood pressure and reduction in hematologic risk factors of diabetes in female patients with T2DM. Further studies in both genders are needed to generalize these findings to total population.

Antioxidant status in peri- and postmenopausal women

Menopause is a risk factor for oxidative stress. The aim of our study is to assess antioxidant system parameters (α-tocopherol, retinol, reduced glutathione, total antioxidant activity) in peri- and postmenopausal women. The antioxidant defense activity by estimation of total antioxidant activity, α-tocopherol, retinol, oxidized and reduced glutathione levels was studied in women of reproductive age (n=37), in perimenopausal (n=41) and postmenopausal women (n=41). In our study we used spectrofluorofotometer methods. Statistical analysis was performed by non-parametric tests with p<0.05 as the level of significance. The results of our study showed the decrease of α-tocopherol and retinol concentrations and the increase of oxidized glutathione level in blood serum both in perimenopausal and postmenopausal women, the total antioxidant activity of blood serum was decreased in postmenopausal women only. The results of our study demonstrate that decrease of antioxidant defense system resources depends on the menopausal phase.

Association between the serum concentration of triiodothyronine with components of metabolic syndrome, cardiovascular risk, and diet in euthyroid post-menopausal women without and with metabolic syndrome

PURPOSE

To determine the association between the serum concentration of triiodothyronine (T3) with components of metabolic syndrome (MetS), cardiovascular risk (CVR), and diet in euthyroid post-menopausal women without and with MetS.

METHODS

A cross-sectional study was performed in 120 voluntary women of an indigenous population from Tlaxcala-México. Euthyroid status was assessed measuring the serum concentration of thyrotropin (TSH) and thyroid hormones, while that of estradiol was measured to confirm the postmenopausal condition. MetS was diagnosed using the American Heart Association/National Heart, Lung, and Blood Institute Scientific Statement (AHA/NHLBI) criterion. Estimation of CVR was calculated based on the Framingham scale. Diet components were evaluated based on survey applications. Correlations, logistic regression analyses, ANOVA or Kruskall-Wallis, and chi-square tests were used to determine significant differences (P ≤ 0.05) between women without MetS and women with MetS having different serum concentrations of T3.

RESULTS

Triiodothyronine was positively correlated with insulin but negatively correlated with glucose, high-density lipoprotein cholesterol (HDL-C), and CVR. Compared to women without MetS, women with MetS and low-normal T3 concentration showed a high risk for hyperglycemia and moderate/high risk for CVR. In contrast, a high-normal T3 concentration increased the risk to have a big waist circumference, a high concentration of HDL-C, and insulin resistance. Diet analysis showed a high grade of malnutrition in women from all groups. The intake of calories was positively affected by the T3 concentration, albeit it did not affect the extent of malnutrition.

CONCLUSIONS

In contrast to concentrations of TSH, total thyroxin (T4), and free T4, the concentration of serum T3 was strongly correlated with cardio-metabolic variables in euthyroid postmenopausal women. In comparison to women without MetS, a high-normal serum concentration of T3 in women with MetS is positively associated with reduced glycaemia and CVR but negatively related to body mass index (BMI), insulin, insulin resistance, and HDL-C. Although the analyzed population had a nutritional deficiency, both calories and iron intake were positively affected by the T3 concentration. Our results suggest the necessity of health programs monitoring T3 in old people in order to treat hyperglycemia, cardio-metabolic components, and the ageing anorexia.