Physicochemical, technofunctional, in vitro antioxidant, and in situ muscle protein synthesis properties of a sprat (Sprattus sprattus) protein hydrolysate

Introduction

Sprat (Sprattus sprattus) is an underutilized fish species that may act as an economic and sustainable alternative source of protein due to its good amino acid (AA) profile along with its potential to act as a source of multiple bioactive peptide sequences.

Method and results

This study characterized the physicochemical, technofunctional, and in vitro antioxidant properties along with the AA profile and score of a sprat protein enzymatic hydrolysate (SPH). Furthermore, the impact of the SPH on the growth, proliferation, and muscle protein synthesis (MPS) in skeletal muscle (C2C12) myotubes was examined. The SPH displayed good solubility and emulsion stabilization properties containing all essential and non-essential AAs. Limited additional hydrolysis was observed following in vitro-simulated gastrointestinal digestion (SGID) of the SPH. The SGID-treated SPH (SPH-SGID) displayed in vitro oxygen radical antioxidant capacity (ORAC) activity (549.42 μmol TE/g sample) and the ability to reduce (68%) reactive oxygen species (ROS) production in C2C12 myotubes. Muscle growth and myotube thickness were analyzed using an xCELLigence™ platform in C2C12 myotubes treated with 1 mg protein equivalent.mL^-1 of SPH-SGID for 4 h. Anabolic signaling (phosphorylation of mTOR, rpS6, and 4E-BP1) and MPS (measured by puromycin incorporation) were assessed using immunoblotting. SPH-SGID significantly increased myotube thickness (p < 0.0001) compared to the negative control (cells grown in AA and serum-free medium). MPS was also significantly higher after incubation with SPH-SGID compared with the negative control (p < 0.05).

Conclusions

These preliminary in situ results indicate that SPH may have the ability to promote muscle enhancement. In vivo human studies are required to verify these findings.

A Cell-Based Assessment of the Muscle Anabolic Potential of Blue Whiting (Micromesistius poutassou) Protein Hydrolysates

Blue whiting (BW) represents an underutilised fish species containing a high-quality protein and amino acid (AA) profile with numerous potentially bioactive peptide sequences, making BW an economic and sustainable alternative source of protein. This study investigated the impact of three different BW protein hydrolysates (BWPH-X, Y and Z) on growth, proliferation and muscle protein synthesis (MPS) in skeletal muscle (C2C12) myotubes. BWPHs were hydrolysed using different enzymatic and heat exposures and underwent simulated gastrointestinal digestion (SGID), each resulting in a high degree of hydrolysis (33.41-37.29%) and high quantities of low molecular mass peptides (86.17-97.12% <1 kDa). C2C12 myotubes were treated with 1 mg protein equivalent/mL of SGID-BWPHs for 4 h. Muscle growth and myotube thickness were analysed using an xCelligence™ platform. Anabolic signalling (phosphorylation of mTOR, rpS6 and 4E-BP1) and MPS measured by puromycin incorporation were assessed using immunoblotting. BWPH-X significantly increased muscle growth (p < 0.01) and myotube thickness (p < 0.0001) compared to the negative control (amino acid and serum free media). Muscle protein synthesis (MPS), as measured by puromycin incorporation, was significantly higher after incubation with BWPH-X compared with the negative control, but did not significantly change in response to BWPH-Y and Z treatments. Taken together, these preliminary findings demonstrate the anabolic potential of some but not all BWPHs on muscle enhancement, thus providing justification for human dietary intervention studies to confirm and translate the results of such investigations to dietary recommendations and practices.

Impact of lifetime concentration of mannose on renal function: insights from Mendelian randomization

Background

Mannose is a sugar monomer of the aldohexose series of carbohydrates, important in human metabolism, especially in the glycosylation of certain proteins. There is a handful of controversial data from observational studies on the serum levels of mannose and risks of renal disease.

Purpose

We performed a Mendelian Randomization (MR) analysis to obtain unconfounded estimates of the casual associations between genetically instrumented serum mannose, estimated glomerular filtration rate (eGFR) and the risk for chronic kidney disease (CKD defined as eGFR &lt;60 ml/min/1.73 m2).

Methods

MR was implemented by using summary-level data from the largest ever genome-wide association studies (GWAS) conducted on serum mannose and renal function. Inverse variance weighted method (IVW), weighted median (WM)-based method, MR-Egger, MR-Robust Adjusted Profile Score (RAPS), MR-Pleiotropy RESidual Sum and Outlier (PRESSO) were also applied. Sensitivity analysis was conducted using the leave-one-out method. The analyses were performed in the total population, in non-diabetics and in patients with type 2 diabetes mellitus (T2DM).

Results

Serum mannose concentrations were not significantly associated with CKD risk (IVW: beta=1.018, p=0.273), but they were negatively related to eGFR in the total population (IVW: beta=−0.137, p=0.003), the non-diabetics (IVW: beta=−0.126, p=0.018) and the T2DM patients (IVW: beta=−0.344, p=0.004). None of the MR-Egger estimates showed heterogeneity, and the MR-PRESSO analysis did not find any possibility of outliers for all of the estimates. The pleiotropy test also indicated a low chance of pleiotropy for all estimations (p&gt;0.242), as did the MR-RAPS analysis. Leave-one-out method demonstrated that the observed associations were not driven by single-nucleotide polymorphisms.

Conclusions

Our results highlighted that individuals with genetically higher serum mannose levels have a significantly lower eGFR, regardless of the presence or absence of T2DM. However, no association between serum mannose concentrations and the risk of CKD was observed.

Funding Acknowledgement

Type of funding sources: None.

Relationship between low-density lipoprotein cholesterol, lipid-lowering agents and risk of stroke: a meta-analysis of observational studies (n = 355,591) and randomized controlled trials (n = 165,988)

INTRODUCTION

The impact of low-density lipoprotein cholesterol (LDL-C) on the risk of different types of strokes is unclear. Therefore, we systematically evaluated the impact of LDL-C levels (cohort studies) and lipid-lowering agents (LLAs) (randomized controlled trials) on the different types of stroke.

MATERIAL AND METHODS

PubMed, SCOPUS, Web of Science and Google Scholar were searched up to 1^st September 2019. The DerSimonian-Laird method and generic inverse variance methods were used for quantitative data synthesis. The leave-one-out method was performed as sensitivity analysis. Trial sequential analysis (TSA) was used to evaluate the optimal sample size to detect a 35% reduction in outcomes after administration of LLAs.

RESULTS

Participants in the highest category of LDL-C had a lower risk of hemorrhagic stroke (RR = 0.91, 95% CI: 0.85-0.98, I ² = 0%) compared with the lowest category of LDL-C. Subjects with the highest category of LDL-C had a higher risk of ischemic stroke (RR = 1.11, 95% CI: 1.07-1.14, I ² = 0%) compared to the lowest LDL-C category. LLAs decreased the risk of all types of strokes for those who achieved LDL-C < 1.8 mmol/l (< 70 mg/dl; RR = 0.88, 95% CI: 0.80-0.96, absolute risk reduction (ARR): 0.7%, number needed to treat (NNT): 143, I ² = 53%, n = 13). Statin therapy decreased the risk of all strokes (RR = 0.88, 95% CI: 0.80-0.97, ARR = 0.6%, NNT = 167, I ² = 56%). With regard to ischemic stroke only, LLAs decreased the risk of ischemic stroke for those who achieved LDL-C < 1.8 mmol/l (< 70 mg/dl; RR = 0.75, 95% CI: 0.67-0.83, ARR = 1.3%, NNT = 77, I ² = 0%); the same was observed for statins (RR = 0.76, 95% CI: 0.69-0.84, ARR = 1.3%, NNT = 77, I ² = 32%). TSA indicated that both benefit boundaries and optimal sample size were reached. There was no significant effect of LLAs regardless of the achieved level of LDL-C on the risk of hemorrhagic stroke; however, TSA indicated that further studies are needed to settle the question and most of the effects were subject to high levels of heterogeneity.

CONCLUSIONS

Our study sheds light on the debatable association between low LDL-C and different type of strokes. This information can help determine the optimal LDL-C range for stroke prevention, and help plan future LLA studies.

Omega-6 fatty acids and the risk of cardiovascular disease: insights from a systematic review and meta-analysis of randomized controlled trials and a Mendelian randomization study

INTRODUCTION

Omega-6 polyunsaturated fatty acids (PUFAs) represent almost 15% of the total energy intake in Western countries. Their effects on the cardiovascular (CV) risk factors are still controversial. Thus, we performed a systematic review and meta-analysis of randomized control trials (RCTs) as well as a Mendelian randomization (MR) analysis to evaluate the links and possible causality between supplementation or serum levels of omega-6 PUFA, CV disease (CVD) and cardiometabolic risk factors.

MATERIAL AND METHODS

Selected databases were searched until September 2019 to identify prospective studies investigating the effects of omega-6 PUFA supplementation on CVD events/mortality. Random-effects model meta-analysis was performed for quantitative data synthesis. Trial sequential analysis (TSA) was used to evaluate the optimal sample size to detect a 20% reduction in outcomes after administration of omega-6 PUFAs. The inverse variance weighted (IVW) method, weighted median-based method, MR-Egger and MR-Pleiotropy RESidual Sum and Outlier (PRESSO) were applied for MR.

RESULTS

The pooled estimate risk ratio (RR) of omega-6 PUFA supplementation was 0.94 for any CVD event (95% CI: 0.77-1.15, I ² = 66.2%), 1.06 for CVD death (95% CI: 0.73-1.55, I ² = 66.2%), 0.84 for coronary heart disease (CHD) events (95% CI: 0.61-1.16, I ² = 79.4%), 0.87 for myocardial infarction (MI) (95% CI: 0.74-1.01, I ² = 2.3%) and 1.36 for stroke (95% CI: 0.45-4.07, I ² = 55.3%). In contrast, MR showed that individuals with higher serum omega-6 acid - adrenic acid (AA) levels had a greater risk for CHD events (IVW β = 0.526), MI (IVW β = 0.606) and large artery stroke (IVW β = 1.694), as well as increased levels of fasting blood glucose (FBG) (IVW β = 0.417), low-density lipoprotein cholesterol (LDL-C) (IVW β = 0.806), high-density lipoprotein cholesterol (HDL-C) (IVW β = 0.820), and lower levels of triglycerides (TG) (IVW β = -1.064) and total cholesterol (TC) (IVW β = -1.064).

CONCLUSIONS

Omega-6 PUFA supplementation did not affect the risk for CVD morbidity and mortality. Additionally, based on MR analysis we found that higher AA levels might even significantly increase the risk of CHD, MI and large artery stroke, as well as the levels of FBG and LDL-C, whereas they were negatively associated with TC and TG. Since a considerable chance of heterogeneity was observed for some of the results, further research is needed to elucidate the effects of omega-6 PUFAs on cardiometabolic outcomes.

Longer sleep duration may negatively affect renal function

BACKGROUND

Observational studies evaluating the link between sleep duration and kidney function reported controversial results. In the present study, Mendelian randomization analysis was applied to obtain unconfounded estimates of the casual association of genetically determined sleep duration with estimated glomerular filtration rate and the risk of chronic kidney disease.

METHODS

Data from the largest genome-wide association studies on self-reported and accelerometer-derived sleep duration, estimated glomerular filtration rate and chronic kidney disease were analysed in total, as well as separately in diabetic and non-diabetic individuals. Inverse variance weighted (IVW) method, weighted median-based method, MR-Egger and MR-Pleiotropy RESidual Sum and Outlier (MR-PRESSO) were applied, as well as the leave-one-out method to rule out the impact of single single-nucleotide polymorphism.

RESULTS

Individuals with genetically longer self-reported sleep duration had a higher chronic kidney disease risk (IVW: β = 0.358, p = 0.047). Furthermore, in non-diabetics, longer self-reported sleep duration was negatively associated with estimated glomerular filtration rate (IVW: β = - 0.024, p = 0.020). Similarly, accelerometer-derived sleep duration was negatively related to estimated glomerular filtration rate in the total population (IVW: β = - 0.019, p = 0.047) and then on-diabetic individuals. No significant association was found between self-reported sleep duration and estimated glomerular filtration rate in the whole population and type-2 diabetes mellitus patients. None of the estimated associations was subjected to a significant level of heterogeneity. MR-PRESSO analysis did not show any chance of outliers for all estimates. The pleiotropy test also indicated low chance of pleiotropy. The leave-one-out method demonstrated that the links were not driven by single-nucleotide polymorphisms.

CONCLUSIONS

For the first time, the present study shed a light on the potential harmful effects of longer sleep duration (measured both objectively and subjectively) on kidney function. This finding was observed in the total population and in non-diabetic individuals, but not in those with diabetes. Further research is needed to elucidate the links between sleep duration, estimated glomerular filtration rate and the risk of chronic kidney disease.

Serum anti-inflammatory and inflammatory markers have no causal impact on telomere length: a Mendelian randomization study

INTRODUCTION

The relationship between inflammatory and anti-inflammatory markers and telomere length (TL), a biological index of aging, is still poorly understood. By applying a 2-sample Mendelian randomization (MR), we investigated the causal associations between adiponectin, bilirubin, C-reactive protein (CRP), leptin, and serum uric acid (SUA) with TL.

MATERIAL AND METHODS

MR was implemented by using summary-level data from the largest ever genome-wide association studies (GWAS) conducted on our interested exposure and TL. Inverse variance weighted method (IVW), weighted median (WM)-based method, MR-Egger, MR-Robust Adjusted Profile Score (RAPS), and MR-Pleiotropy RESidual Sum and Outlier (PRESSO) were applied. Sensitivity analysis was conducted using the leave-one-out method.

RESULTS

With regard to adiponectin, CRP, leptin, and SUA levels, we found no effect on TL for all 4 types of tests (all p > 0.108). Results of the MR-Egger (p = 0.892) and IVW (p = 0.124) showed that bilirubin had no effect on telomere maintenance, whereas the results of the WM (p = 0.030) and RAPS (p = 0.022) were negative, with higher bilirubin concentrations linked to shorter TL. There was a low likelihood of heterogeneity for all the estimations, except for bilirubin (IVW p = 0.026, MR Egger p = 0.018). MR-PRESSO highlighted no outlier. For all the estimations, we observed negligible intercepts that were indicative of low likelihood of the pleiotropy (all p > 0.161). The results of leave-one-out method demonstrated that the links are not driven because of single nucleotide polymorphisms (SNPs).

CONCLUSIONS

Our results highlight that neither the anti-inflammatory nor pro-inflammatory markers tested have any significant causal effect on TL. The casual role of bilirubin on TL still needs to be investigated.

Longer sleep duration may negatively affect renal function

Background

Observational studies evaluating the link between sleep duration and kidney function reported controversial results. In the present study, Mendelian Randomization (MR) analysis was applied to obtain unconfounded estimates of the casual association of genetically determined sleep duration with estimated glomerular filtration rate (eGFR) and the risk of chronic kidney disease (CKD).

Methods

Data from the largest genome-wide association studies (GWAS) on self-reported and accelerometer derived sleep duration, eGFR and CKD were analysed in total, as well as separately in diabetic and non-diabetic individuals. Inverse variance weighted method (IVW), weighted median (WM)-based method, MR-Egger, as well as MR-Pleiotropy RESidual Sum and Outlier (PRESSO) were applied. To rule out the impact of single single-nucleotide polymorphism (SNP), the leave-one-out method was used.

Results

Overall, individuals with genetically longer self-reported sleep duration had a higher CKD risk (IVW: beta=0.358, p=0.047). Furthermore, in non-diabetics, longer self-reported sleep duration was negatively associated eGFR (IVW: beta=−0.024, p=0.020). Similarly, accelerometer derived sleep duration was negatively related to eGFR in the total population (IVW: beta=−0.019, p=0.047) and the non-diabetic individuals (IVW: beta=−0.025, p=0.014) (Table). No significant association was found between self-reported sleep duration and eGFR in the whole population (IVW: beta=−0.019, p=0.072) and T2DM patients (IVW: beta=0.028, p=0.484). None of the estimated associations was subjected to a significant level of heterogeneity. Furthermore, MR-PRESSO analysis did not show any chance of outliers for all estimates. The pleiotropy test, with very negligible intercept and insignificant p value. The results of the MR-RAPS were identical with the IVW estimates, highlighting again no possibility of pleiotropy. The leave-one-out method demonstrated that the links were not driven by single SNPs.

Conclusions

For the first time, the present study shed a light on the potential harmful effects of longer sleep duration (measured both objectively and subjectively) on kidney function. This finding was observed in the total population and in non-diabetic individuals, but not in those with diabetes. Further research is needed to elucidate the links between sleep duration, eGFR and CKD.

Funding Acknowledgement

Type of funding source: None

Omega-6 fatty acids and risk of cardiovascular disease: insight from systematic review and meta-analysis of randomized controlled trials and a mendelian randomization study

Background

Omega-6 polyunsaturated fatty acids (PUFAs) represent almost 15% of the total energy intake in the Western countries. Their effects on several cardiovascular (CV) risk factors are still controversial.

Purpose

We performed a systematic review and meta-analysis of randomized control trials (RCTs) as well as a Mendelian randomization (MR) analysis to evaluate the links (or possible causality) between supplementation or serum levels of omega-6 PUFA, CV disease (CVD) and cardiometabolic risk factors.

Methods

Selected databases were searched until 31 August 2019 to identify prospective studies investigating the effects of omega-6 PUFAs supplementation on CVD events/mortality. Random-effects model meta-analysis was performed for quantitative data synthesis. Trial sequential analysis (TSA) was used to evaluate the optimal sample size to detect a 20% reduction in outcomes after administration of omega-6 PUFAs. Inverse variance weighted method (IVW), weighted median-based method, MR-Egger and MR-Pleiotropy RESidual Sum and Outlier (PRESSO) were applied for MR.

Results

In the meta-analysis of 9 studies with 4,433 participants we showed that omega-6 PUFAs supplementation was not associated with CVD event risk - RR 0.94 (95% CI: 0.77–1.15, heterogeneity p=0.031; I2=66.2%, n=4 studies). The pooled estimate (RR) of the effect of omega-6 PUFAs supplementation on CVD death was 1.06 (95% C:I 0.73–1.55, heterogeneity p=0.011; I2=66.2%, n=6 studies), on CHD events 0.84 (95% CI: 0.61–1.16, heterogeneity p=0.001; I2=79.4%), on MI 0.87 (95% CI: 0.74–1.01, heterogeneity p=0.381; I2=2.3%) (Figure), and on stroke 1.36 (95% CI: 0.45–4.07, heterogeneity p=0.082; I2=55.3%). In MR analysis we showed that individuals with genetically higher serum adrenic acid (AA; 22:4, n-6) levels had a greater risk of CHD events (IVW=Beta: 0.526, p=0.007), MI (IVW=Beta: 0.606, p=0.017) and stroke (IVW=Beta: 1.694, p=0.009), as well as higher levels of FBG (IVW=Beta: 0.417, p=1.0x10–3), LDL-C (IVW=Beta: 0.806, p=4.9x10–5), HDL-C (IVW=Beta: −0.820, p=4.3x10–17), whereas lower levels of TG (IVW=Beta: −1.064, p=1.2x10–12) and TC (IVW=Beta: −1.064, p=1.2x10–12).

Conclusions

In the pooled analysis different omega-6 PUFAs supplementation did not affect the risk of MI, stroke and CHD event/mortality or the serum concentration of cardiometabolic parameters (data not presented), however in MR analysis, higher AA levels significantly associated with the risk of CHD, MI and stroke, as well as with elevated levels of FBG, LDL-C and HDL-C and reduced levels of TC and TG. There is probably lack of class effect for omega-6 PUFAs, therefore further studies are needed to assess the effects of omega-6 PUFAs on cardiometabolic outcomes.

Funding Acknowledgement

Type of funding source: None

Monounsaturated Fatty Acid Levels May Not Affect Cardiovascular Events: Results From a Mendelian Randomization Analysis

Background/Aim: Several observational studies evaluated the links between serum monounsaturated fatty acids (MUFAs) and cardiovascular events with controversial results. In the present study, Mendelian randomization (MR) analysis was applied to obtain unconfounded estimates of the causal associations of genetically determined serum MUFAs with coronary heart disease (CHD), myocardial infarction (MI), cardioembolic stroke (CS), and ischemic stroke (IS).

Methods: Four MUFAs were studied (i.e., 10-heptadecenoate, myristoleic, oleic, and palmitoleic acid). Data from the largest genome-wide association studies on MUFAs, CHD, MI, and stroke were analyzed. Inverse variance weighted method (IVW), weighted median (WM)-based method, MR-Egger, as well as MR-pleiotropy residual sum and outlier were applied. To rule out the impact of single-nucleotide polymorphism (SNP), the leave-one-out method was also performed.

Results: Genetically higher-serum 10-heptadecenoate levels did not affect the risk of CHD (IVW = Beta: −0.304, p = 0.185), MI (IVW = Beta: −0.505, p = 0.066), CS (IVW = Beta: −0.056, p = 0.945), and IS (IVW = Beta: −0.121, p = 0.767). Similarly, no significant associations were observed for myristoleic acid (CHD: IVW = Beta: 0.008; MI: IVW = Beta: 0.041; CS: IVW = Beta: 0.881; IS: IVW = Beta: 0.162), oleic acid (CHD: IVW = Beta: −0.2417; MI: IVW = Beta: −0.119; CS: IVW = Beta: 1.059; IS: IVW = Beta: 0.008491), and palmitoleic acid (CHD: IVW = Beta: −0.06957; MI: IVW = Beta: −0.01255; CS: IVW = Beta: 1.042; IS: IVW = Beta: −0.1862). A low likelihood of heterogeneity and pleiotropy was reported, and the observed associations were not driven by single SNPs.

Conclusions: In the present MR analysis, serum MUFA levels were not associated with the risk of CHD, MI, CS, and IS. Further research, evaluating more MUFAs, is required to elucidate the links between MUFAs and CVD to contribute to health policy decisions in reducing CVD risk.

Adverse Impact of Desulfovibrio spp. and Beneficial Role of Anaerostipes spp. on Renal Function: Insights from a Mendelian Randomization Analysis

Background: The microbiota composition is now considered as one of the main modifiable risk factors for health. No controlled study has been performed on the association between microbiota composition and renal function. We applied Mendelian randomization (MR) to estimate the casual impact of eight microbiota genera on renal function and the risk of chronic kidney disease (CKD). Methods: MR was implemented by using summary-level data from the largest-ever genome-wide association studies (GWAS) conducted on microbiota genera, CKD and renal function parameters. The inverse-variance weighted method (IVW), weighted median (WM)-based method, MR-Egger, MR-Robust Adjusted Profile Score (RAPS), MR-Pleiotropy RESidual Sum and Outlier (PRESSO) were applied. A sensitivity analysis was conducted using the leave-one-out method. Results: The Anaerostipes genus was associated with higher estimated glomerular filtration rate (eGFR) in the overall population (IVW: β = 0.003, p = 0.021) and non-diabetes mellitus (DM) subgroup (IVW: β = 0.003, p = 0.033), while it had a non-significant association with the risk of CKD and eGFR in DM patients. Subjects with higher abundance of Desulfovibrio spp. had a significantly lower level of eGFR (IVW: β = −0.001, p = 0.035); the same results were observed in non-DM (IVW: β = −0.001, p = 0.007) subjects. Acidaminococcus, Bacteroides, Bifidobacterium, Faecalibacterium, Lactobacillus and Megamonas had no significant association with eGFR in the overall population, DM and non-DM subgroups (IVW: p > 0.105 for all groups); they also presented no significant association with the risk of CKD (IVW: p > 0.201 for all groups). Analyses of MR-PRESSO did not highlight any outlier. The pleiotropy test, with very negligible intercept and insignificant p-value, also indicated no chance of pleiotropy for all estimations. The leave-one-out method demonstrated that the observed links were not driven by single single-nucleotide polymorphism. Conclusions: Our results suggest an adverse association of Desulfovibrio spp. and a beneficial association of Anaerostipes spp. with eGFR. Further studies using multiple robust instruments are needed to confirm these results.

Smoking Discriminately Changes the Serum Active and Non-Active Forms of Vitamin B12

Smoking may modify the appetite, and consequently affect nutrient intake and serum micronutrients. The effect of smoking on vitamin B12 status has been considered in several studies. The research proposed that organic nitrites, nitro oxide, cyanides, and isocyanides of cigarette smoke interfere with vitamin B12 metabolism, and convert it to inactive forms. This research was carried out to determine the serum level of active and inactive forms of vitamin B12 in male smokers in comparison with male nonsmokers. This is a case-control study, in which the participants were 85 male smokers and 85 male nonsmokers. The serum levels of total and active form of vitamin B12 were measured. Dietary intake was recorded by a quantitative food frequency questionnaire and one-day 24-hour dietary recall method. Independent two sample T test was used to compare quantitative variables between the case and control groups. The serum level of total vitamin B12 was not significantly different between two groups, but serum level of active form of vitamin B12 in the smoking group was significantly lower than non-smoking group (P<0.001). This is one of the first studies that evaluated the serum level of active form of vitamin B12 in smokers in the Iranian community. The results of this study identified that serum level of total vitamin B12 might be not different between smoking and non-smoking people, but the function of this vitamin is disturbed in the body of smokers through the reduction of serum level of active form of vitamin B12.