Scientific update on B vitamins: Folate/folic acid and interactions with other B vitamins Helene McNulty Northern Ireland Centre for Food and Health (NICHE) University of Ulster Folate/folic acid and interactions with other B vitamins This talk will cover Folate/folic acid and metabolically related B vitamins Role of optimal B vitamin status in health maintenance Challenges 1
Folate and related B vitamins Have a major metabolic role in methylation processes Prevent homocysteine accumulation Health benefits of B-vitamins may relate to their homocysteine-lowering effects or be independent of homocysteine Methionine Diet Folate Cycle Methyl Acceptor Methylated Acceptor S-Adenosylhomocysteine S-Adenosylmethionine Homocysteine B6 Cystathionine β- Synthase Cystathionine B12 Tetrahydrofolate Methionine Synthase Folate 5,10 Methylene Tetrahydrofolate MTHFR B2 NADP* Remethylation pathway NADPH Trans-sulfuration Pathway Cysteine Sulfate + H 2 0 Urine Homocysteine Metabolism 2
Optimal folate and related B-vitamin status Role in maintaining health Evidence Maternal health in pregnancy conclusive Foetal development conclusive Cognitive health in childhood early evidence Prevention of heart disease/stroke convincing Cancer prevention promising Bone health possible role Cognitive function in ageing possible role Elevated homocysteine as a risk factor for CVD (story until 2004) similar magnitude of risk to that of elevated cholesterol an independent risk factor, but may enhance the effect of conventional risk factors estimated 1,2 that a lowering of homocysteine by 3 µmol/l would reduce the risk of coronary heart disease by 11-16% stroke by 19-24% 1 The Homocysteine Studies Collaboration. 2002 JAMA; 288:2015-2022. 2 Wald et al. 2002 BMJ; 325:1202-08 3
Clinical trials of homocysteine-lowering and CVD events Vitamin Intervention for Stroke Prevention (VISP) Randomized Controlled Trial. Toole et al. JAMA 2004;291:565-575. Heart Outcomes Prevention Evaluation 2 (HOPE-2). Lonn et al. N Engl J Med 2006;354:1567-1577. The Norwegian Vitamin Trial (NORVIT). Bonaa et al. N Engl J Med 2006; 354:1578-1588. The Western Norway B-vitamin Intervention Trial (WENBIT). Ebbing et al. JAMA. 2008;300:795-804. The Women s Antioxidant and Folic Acid Cardiovascular Study (WAFACS). Albert et al. JAMA 2008; 299:2027-2036. Study of the effectiveness of Additional Reductions in Cholesterol and Homocysteine (SEARCH) Collaborative Group. JAMA 2010; 303:2486-2494 Clinical Trials of homocysteine-lowering HOPE 2 Investigators 2006 NEJM;354:1567-77 Relative risk (95% CI) P value Primary outcomes Composite of death (all vascular disease) 0.95 (0.84-1.07) 0.41 Death from Cardiovascular causes 0.96 (0.81-1.13) 0.59 Myocardial infarction 0.98 (0.85-1.14) 0.82 Stroke 0.75 (0.59-0.97) 0.03 4
Randomized Trials of homocysteine-lowering/ folic acid and risk of stroke: a meta-analysis Wang et al 2007 Lancet;369:1876-82 Relative risk (95% CI) P value Overall 0.82 (0.68-1.00) 0.045 Duration of intervention 36 months >36 months 1.00 (0.83-1.21) 0.71 (0.57-0.87) 0.95 0.001 Homocysteine lowering <20% 20% 0.89 (0.55-1.42) 0.77 (0.63-0.94) 0.62 0.012 History of stroke Yes No 1.04 (0.84-1.29) 0.75 (0.62-0.90) 0.71 0.002 Randomized Trials of homocysteine-lowering/ B-vitamins and risk of stroke: a meta-analysis Lee et al 2010 Stroke; 41:1205-1212 Relative risk (95% CI) P value Overall 0.93 (0.85-1.03) 0.16 Duration of intervention <3 years 3 years Homocysteine lowering <20% 20% Stroke prevention Secondary Non-secondary 1.03 (0.84-1.27) 0.87 (0.78-0.98) 1.02 (0.86-1.22) 0.87 (0.77-0.98) 1.04 (0.84-1.29) 0.89 (0.79-0.99) NS 0.02 NS 0.02 NS 0.03 Gender Effect Predominantly Women Predominantly Men 1.11 (0.83-1.49) 0.84 (0.74-0.94) NS 0.003 5
Decline in stroke related mortality in the US and Canada Yang et al 2006 Circulation;113:1335-43 Genetic Studies Is MTHFR 677C T Polymorphism a risk factor for CVD? Most important genetic determinant of elevated homocysteine Meta-analyses 1,2,3 ( > 25,000 CVD cases) estimate a 14-21% excess CVD risk in homozygous individuals (TT genotype), but large geographical variation between countries Consistency between increasing trends of CVD risk among individuals with CC vs CT vs TT genotypes homocysteine concentrations among 3 genotypes Good evidence for a causal relationship between homocysteine and CVD Wald DS et al. BMJ 2002; 325: 1202 1206. Klerk et al. JAMA 2002; 288: 2023 2031. Lewis et al. BMJ 2005; 331: 1053 1056. 6
Methionine Diet Folate Cycle Methyl Acceptor Methylated Acceptor S-Adenosylhomocysteine S-Adenosylmethionine Homocysteine B6 Cystathionine β- Synthase Cystathionine B12 Tetrahydrofolate Methionine Synthase Folate 5,10 Methylene Tetrahydrofolate MTHFR B2 NADP* Remethylation pathway NADPH Trans-sulfuration Pathway Cysteine Sulfate + H 2 0 Urine Homocysteine Metabolism Methylenetetrahydrofolate reductase (MTHFR) SUBSTRATE: PRODUCT: 5,10 Methylenetetrahydrofolate 5 Methyltetrahydrofolate COFACTOR: Flavin Adenine Dinucleotide (FAD) PRECURSOR: Riboflavin (vitamin B-2) Polymorphic mutations in MTHFR MTHFR 677C T Polymorphism C to T substitution at base pair 677 Alanine/valine change in the amino acid sequence Functionally defective enzyme 7
Effect of riboflavin intervention on homcysteine in people with TT genotype McNulty et al Circulation 2006;113:74-80 Mean homocysteine (µmol/l) CC CT TT (n = 27) (n = 26) (n = 34) Baseline 10.7 12.2 17.6 After intervention 10.9 11.8 13.0 Cardiovascular Mortality Risk Systolic/Diastolic Blood Pressure (mmhg) Lewington S et al Lancet 2002;360:1903-1913 Chobanian AV et al JAMA 2003;289:2560-2572 8
Recent results on this gene-nutrient interaction Horigan et al 2010 J Hypertension 28:478-486 Patients with TT genotype appeared resistant to conventional antihypertensive drugs Only 37% achieved target BP of <140/90; 2-fold higher rate of hypertension vs CC genotype Riboflavin (1.6 mg/d) reduced systolic and diastolic blood pressure specifically in those with the TT genotype: 143/88 to 131/80 (p<0.01) 9
MTHFR 677 TT genotype and BP In people with TT genotype, MTHFR enzyme less active Higher riboflavin status through * Natural sources e.g. high milk intake * Intervention with B2 supplement MTHFR enzyme more active Plasma Homocysteine Blood Pressure Decreased Decreased Blood Pressure Decreased Age Specific Prevalence of Dementia (all types) % Age Group (Years) 10
Risk Factors: cognitive decline and dementia Head Trauma BP Age Cholesterol Education level Nutritional Status BMI Smoking Cognitive Decline Genetic Physical Activity Gender Depression Kivipelto et al Lancet Neurol 2006; 5: 735-41 RCTs of B-vitamins and cognitive function in older people Reference Sample Treatment Outcome McMahon et al NEJM 2006; 354: 2764-72 n=276 Healthy people >65 y Combined B vitamins (folic acid/b12/b6) or placebo for 2 years No improvement in cognitive performance Durga et al Lancet 2007; 369:208-16 n=818 Healthy people 50-70 y Folic acid or placebo for 3yrs Significant improvement in memory information processing sensorimotor speed Smith et al PLoS ONE 2010; 5: e12244 n=168 Patients with mild cognitive impairment Combined B vitamins (folic acid/b12/b6) or placebo A significantly reduced rate of brain atrophy on MRI scan >70 y for 2 years 11
Challenges Folate and related B-vitamins Folate Vitamin B-12 Riboflavin 12
Rates of NTDs per 10 000 births: 1988-98 Botto et al BMJ 2005;330:571-576 Food folates and Folic acid Food folates are reduced molecules predominantly polyglutamates but converted to monoglutamates for absorption Compared with folic acid, food folates are much less stable to cooking much less bioavailable once ingested The potential to optimise folate status by means of natural food folate sources is very limited 13
Dietary Folate Equivalents (DFE) Dietary Folate Equivalents (DFE) now used in the United States based on differences in bioavailability between natural folates and added folic acid DFE=µg natural food folate + 1.6 times µg FA Deficient and sub-optimal vitamin B12 status High prevalence of low/deficient B12 status among older people 10%: 65-74 years in UK 20%: >75 years Pernicious anaemia (classical B12 deficiency) explains < 2% of cases Food-bound malabsorption (due to atrophic gastritis) Mild (pre-clinical) cause of B12 deficiency Very common; as high as 45% in some studies 14
Sub-optimal riboflavin status Data from a convenience sample in Northern Ireland and NDNS data of British adults aged 19-64 y NI sample: Males 19-64y (n=215) NDNS Males 19-64y NI Sample: Females 19-64y (n=220) NDNS Females 19-64y EGRac 1.35 ± 0.15 1.38 ± 0.17 1.39 ± 0.18 1.40 ± 0.19 EGRac (erythrocyte glutathione reductase activation coefficient) is a functional indicator of riboflavin status. A higher EGRac ratio indicates lower riboflavin status Homocysteine-related B-vitamins The Challenge The average diet is insufficient in providing optimal folate status to lower homocysteine Low vitamin B12 status is common in older people despite high B12 intakes Some evidence of low riboflavin status in the general population 15
Striking the balance Does dose matter? Folic acid safety and toxicity 1989: A review concluded that daily supplements of 5-10 mg folic acid appear to be well tolerated and without toxicity in normal non-pregnant subjects Butterworth CE and Tamura T AJCN 1989;50:353-8 2008: A review cautions that a high folic acid intake may be harmful for some people Smith et al AJCN 2008;87:517-33 16
Safety concerns of overexposure Historical concern: masking of B-12 deficiency Others high dose folic acid might lead to: an adverse interaction with zinc; decreased therapeutic effect of anticonvulsants; decreased natural killer cell cytotoxicity; twin pregnancy Latest big issue: colorectal cancer (Cole et al 2007; Mason et al 2007; Hirsch et al 2009) prostate cancer (Figueiredo et al 2009) Homocysteine response (%) to FA (0.2-0.8 mg/d) according to initial thcy concentration Tighe et al AJCN 2011; 93, 11-18. Homocysteine response (%) Placebo 0.2mg 0.4mg 0.8mg High initial thcy Low initial thcy 17
Absolute change in homocysteine in response to intervention with folic acid in IHD patients Tighe et al AJCN 2011; 93, 11-18 Homocysteine response (µmol/l ) Placebo 0.2mg 0.4mg 0.8mg 6 week 12 week 26 week Take-home messages Balance of current evidence shows that folic acid has a probable effect in preventing chronic disease, especially stroke is most beneficial in the primary prevention of disease and in those with lowest folate status Folate-related B vitamins (vitamins B-12 and B-6) have additional roles in preventing disease beneficial effects not necessarily via homocysteine-lowering Riboflavin may be important in the treatment/prevention of hypertension specifically in people with the MTHFR 677TT genotype The typical diet is sub-optimal in folate, and possibly in related B-vitamins 18
Folate research at UU The Current Players NICHE Our Collaborators in TCD Sean Strain John Scott Mary Ward Anne Molloy Kristina Pentieva Conal Cunningham The TUDA team The EURRECA team The JINGO project team Clinical Collaborators International Collaborators Owen Finnegan Per Magne Ueland, Norway John Purvis Steve Whitehead, Pennsylvania Tom Trouton Barry Marshall Mark Rollins Folate research at UU PhD Students Past Present Geraldine Cuskelly (1997) Mary Ward (1998) Michelle McKinley (1999) Barbara Wilson (2000) Derek McKillop (2001) Paula Tighe (2004) Geraldine Horigan (2006) Maeve Kerr (2006) Breige McNulty (2007) Nadina Askin (2008) Claire Whittle (2009) Catherine Hughes (2010) Carol Wilson (2010) Leslie Altic Michelle Clarke Rosie Reilly 19