Skip to main content
NCBI home page
NIHPA Author Manuscripts logoLink to NIHPA Author Manuscripts
. Author manuscript; available in PMC: 2016 Mar 1.
Published in final edited form as: Eur J Nutr. 2014 May 3;54(2):235–241. doi: 10.1007/s00394-014-0704-1

High plasma folate is negatively associated with leukocyte telomere length in Framingham offspring cohort

Ligi Paul 1,*, Paul F Jacques 2, Abraham Aviv 3, Ramachandran S Vasan 4, Ralph B D’Agostino 5, Daniel Levy 6, Jacob Selhub 7
PMCID: PMC4218881  NIHMSID: NIHMS592112  PMID: 24793435

Abstract

Purpose

Shortening of telomeres, the protective structures at the ends of eukaryotic chromosomes, is associated with age-related pathologies. Telomere length is influenced by DNA integrity and DNA and histone methylation. Folate plays a role in providing precursors for nucleotides and methyl groups for methylation reactions and has the potential to influence telomere length.

Method

We determined the association between leukocyte telomere length and long-term plasma folate status (mean of 4 years) in Framingham Offspring Study (n=1044, female =52.1%, mean age 59 y) using data from samples collected before and after folic acid fortification. Leukocyte telomere length was determined by Southern analysis and fasting plasma folate concentration using microbiological assay.

Results

There was no significant positive association between long-term plasma folate and leukocyte telomere length among the Framingham Offspring Study participants perhaps due to their adequate folate status. While the leukocyte telomere length in the second quintile of plasma folate was longer than that of the first quintile, the difference was not statistically significant. The leukocyte telomere length of the individuals in the fifth quintile of plasma folate was shorter than that of those in the second quintile by 180 bp (P<0.01). There was a linear decrease in leukocyte telomere length with higher plasma folate concentrations in the upper 4 quintiles of plasma folate (P for trend =0.001). Multivitamin use was associated with shorter telomeres in this cohort (P=0.015).

Conclusions

High plasma folate status possibly resulting from high folic acid intake may interfere with the role of folate in maintaining telomere integrity.

Keywords: Telomere length, folate, multivitamins, folic acid fortification

Introduction

Shortening of the length of telomeres, the protective structures at the ends of eukaryotic chromosomes, has been associated with aging and various age-related diseases including cardiovascular disease, cancer, Alzheimer disease and Parkinson disease [1–5]. Telomere length is influenced by DNA integrity [6] and DNA and histone methylation [7–9]. Damage in telomeric DNA is not repaired efficiently and this can lead to shortening of telomeres [6, 10]. Short telomeres lose their protective function, leading to end to end fusion of chromosomes, and chromosome rearrangements [6, 11]. Folate plays a major role in purine and pyrimidine synthesis [12] and deficiency of folate results in DNA damage [13]. Folate also plays a role in providing methyl groups for the synthesis of methionine, the precursor of S-adenosyl methionine, which is the methyl donor for DNA and histone methylation. Loss of DNA and histone methylation results in loss of telomere length regulation and results in unusually long telomeres without the normal heterochromatin structure which are prone to recombinations [7–9]. Thus folate nutritional status has the potential to influence telomere length. We had previously shown a U-shaped relationship between telomere length of peripheral mononuclear cells and plasma folate status in men [14]. Here longer telomeres were observed both at very low folate status and when folate status was adequate. Since low folate status is associated with DNA hypomethylation in peripheral mononuclear cells [15], the longer telomeres observed at under low folate status is possibly due to loss of telomere length regulation due to DNA hypomethylation and hence not an advantageous feature. A positive relationship between plasma folate and telomere length was observed in a small group of older men [16] and in a cohort that was predominantly women [17]. Folic acid fortification was adopted in the US in 1998 leading to a significant increase in the folate status of the US population [18]. Here we determined the association between leukocyte telomere length and plasma folate status using data from Framingham Offspring Study that included both men and women. A significant proportion of the individuals in our study cohort had been exposed to folic acid fortification, which allowed us to determine if the higher folate status of those exposed to fortification is reflected in their telomere length.

Materials and methods

Subjects

The Framingham Offspring Study was initiated in 1971 and included 5124 men and women, who were the offspring or the spouses of the original Framingham Heart Study cohort [19]. Examinations are conducted and data collected approximately every four years in this cohort. Leukocyte telomere length data were available for 1244 participants of Framingham Offspring Study at the sixth examination (1995–1998). Of these, 200 subjects were excluded in this study due to missing values for folate, BMI, serum creatinine or alcohol intake. This study was approved by the Institutional Review Board of Tufts Medical Center and Boston University Medical Center and has been performed in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki and its later amendments. Written informed consent was obtained from all the subjects. The characteristics of the participants in this study are given in Table 1.

Table 1.

Characteristics of the study population 1

Age, y 59.0 (45, 75)
Female 544 (52.1)
Post-menopausal female 446 (82.0)
Multivitamin users 423 (40.7)
Current smokers 134 (12.8)
BMI, kg/m2 27.2 (21.3, 38.5)
Alcohol use, g/d 4.7 (0, 43.0)
Folic acid fortification status
  No 319 (30.6)
  Yes 431 (41.3)
  Not known 294 (28.1)
Plasma /serum concentrations of metabolites
  Plasma folate nmol/L (n=1044)
    Exam 5 (1991–1995) 13.1 (4.2, 46.0)
    Exam 6 (1995–1998) 22.6 (7.0, 61.4)
    Mean of exams 5&6 (long-term) 18.8 (6.8, 49.9)
  Vitamin B-12 pmol/L 293 (158.3, 544.7)
  PLP (nmol/L) 63.3 (24.9, 275.6)
  Hcy µmol/L 9.0 (5.7, 14.7)
  Creatinine (µmol/L) 102.5 (78.7, 133.5)
Open in a new tab
1

n=1044, except for 4 missing values for multivitamin, values are median (5th, 95th percentiles) or n (%)

Determination of leukocyte telomere length

Leukocyte telomere length [20] was determined from the mean terminal restriction fragment length of chromosomes using a Southern blot procedure for biologically unrelated participants of Framingham Offspring Study at the sixth examination [20].

Plasma analyses

All plasma analyses were conducted on fasting samples. Plasma folate concentration was determined by microbiological assay [21]. When folic acid fortification of cereal grains was adopted in the US, fortification was phased-in during the period between September 1996 and July 1997. Thus exposure to folic acid fortification of those who were examined between October 1996 and August 1997 was not certain [22]. The participants who were examined after September 1997 were exposed to folic acid fortification and thus had an increase in plasma folate status over varying durations prior to sample collection [22]. For these reasons, we used the mean of plasma folate concentration from the fifth (1991–1995) and sixth (1995–1998) examinations which better reflects their long-term plasma folate status for the analyses. Serum concentration of creatinine was determined by the Jaffe reaction [23], vitamin B12 using a radioimmunoassay (Quantaphase II; Bio-Rad, Hercules, CA) and pyridoxal 5’-phosphate (PLP) the active form of vitamin B6 using the tyrosine decarboxylase method [24].

Statistical analyses

We used general linear modeling (analysis of covariance) to determine the association between leukocyte telomere length and long-term plasma folate (in quintile categories), multivitamin use and folic acid fortification status (pre vs post). Adjustments (Tukey) were made for multiple comparisons between long-term plasma folate categories. Linear trend across categories of long-term plasma folate was determined by assigning each participant the median value for the category and modeling this value as a continuous variable. The following covariates that have been shown to be influence telomere length were included in the analysis; age, gender, smoking, alcohol use, menopause, serum creatinine, BMI. We also considered plasma concentrations of vitamin B12 and PLP as covariates in the analyses since they are involved in the one carbon metabolism in which folate plays a central role. But, plasma concentrations of vitamin B12 and PLP were not associated with leukocyte telomere length in this model and hence were not used in further analyses. There was no interaction between gender and long-term folate and hence data analyses were not stratified by gender. When the association of leukocyte telomere length with folic acid fortification was determined, only the individuals who were examined before fortification began and after fortification was complete were included in the analyses, those who were examined during the period when fortification was phased-in were excluded from the analysis. 4 participants with missing multivitamin use data were excluded when the relationship between multivitamin use and telomere length was examined. The analyses were conducted using SAS (version 9.2). Associations with a P value of ≤ 0.05 were considered significant.

Results

The age-related difference in mean leukocyte telomere length in the study population was a decrease of 22 bp per year of age. There was no significant positive association between plasma folate and leukocyte telomere length. While the leukocyte telomere length in the second quintile of plasma folate was longer than that of the first quintile, the difference was not statistically significant. The mean leukocyte telomere length of the individuals in the fifth quintile of plasma folate (6.80 ± 0.04 kb ± SE) was significantly shorter than that of those in the second quintile (6.98 ± 0.04 kb ± SE) (P <0.01) (Fig. 1). Since the overall relationship between plasma folate and leukocyte telomere length was not linear, we performed additional secondary analyses to determine the association between plasma folate and telomere length in the upper 4 quintiles. There was a linear decrease in telomere length across the second through fifth quintiles of plasma folate concentrations (Fig. 1, P for trend =0.001). Concentration of plasma folate was negatively associated with its biochemical marker total homocysteine in plasma (r = −0.2426, P <0.0001).

Fig. 1.

Fig. 1

Open in a new tab

Leukocyte telomere length in participants of Framingham Heart Study Offspring cohort according to quintiles of long-term plasma folate concentration. General linear modeling was used to determine the association between leukocyte telomere length and long-term plasma folate. Values are mean and SE. Labeled mean values with unlike letters differ, P value <0.01. * P for trend =0.001 across second to fifth quintiles. The data were adjusted for age, gender, menopause, smoking, BMI, smoking, alcohol use and serum creatinine

We considered 2 variables that could influence plasma folate concentration among the study participants; exposure to folic acid fortification and multivitamin use (Online resources 1 and 2). The mean leukocyte telomere length of individuals examined before fortification was 6.95 ± 0.04, kb ± SE and those examined after folic acid fortification was 6.88 ± 0.04 , kb ± SE, but this difference was not statistically significant (P=0.14), (Online resource 2). Multivitamin users had a shorter leukocyte telomere length when compared to non-users in this cohort (6.84 ± 0.04 vs 6.93 ± 0.03 kb ± SE; P=0.015), (Online resource 2). Among the individuals in the fifth quintile of long-term plasma folate where leukocyte telomere length was shortest, 83% were multivitamin users (Online resource 1). Since multivitamins contain other components like iron that can negatively influence telomere length [25] we conducted the analysis of leukocyte telomere length vs folate quintiles after excluding multivitamin users. The decrease in telomere length across second through fifth quintile of plasma folate persisted even when multivitamin users were omitted from the analysis (P for trend <0.01).

Discussion

Folate is essential for providing nucleotide precursors necessary for maintaining DNA integrity which in turn influences telomere length [6]. Prior studies have shown an association between telomere length and plasma folate status [14, 16, 17], though one recent study did not find any association between plasma folate or folate intake and telomere length [26]. In the current study of Framingham Offspring cohort, samples had been collected before and after the mandatory folic acid fortification of flour and cereal grains in the US in 1998. Folic acid fortification significantly improved the plasma folate status of this cohort [18] and based on the previous studies we expected to see a positive association between plasma folate concentration and telomere length in this cohort. However there was no significant positive association between plasma folate and telomere length in this cohort. The leukocyte telomere length in the second quintile of long-term plasma folate was longer than that of the first quintile but the difference was not statistically significant (Fig. 1). Contrary to our hypothesis, at higher concentrations, plasma folate appeared to have a negative influence on telomere length (Fig 1). The mean leukocyte telomere length of individuals in the fifth quintile of long-term plasma folate was significantly shorter than those in the second quintile by 180 bp (Fig 1). As a reference for this difference in telomere length due to nutritional status, the difference in leukocyte telomere length due to age, which is a major determinant of telomere length, was a decrease of 22 bp per year of age. The age related difference in telomere length in this study is similar to what has been previously reported for other cohorts [27].

Current literature shows that there is a bell shaped relationship between plasma folate/folate intake and optimal health where both low and high plasma folate/folate intake are associated with negative health outcomes. A similar effect has been reported for selenium intake and health outcomes [28]. Under low folate status there is an increase in risk for neural tube defects and many chronic diseases including many types of cancer, cardiovascular disease and cognitive dysfunction [29–33]. Supplementary folate nutrition has been shown to prevent occurrence of neural tube defects [33] and many countries adopted folic acid fortification for this reason. Folic acid is a synthetic form of the vitamin used in fortified foods and supplements due to its stability. Among men and women over the age of 50 in the 2003–2006 National Health and Nutritional Examination Survey, the mean folic acid intake from supplements alone was 436± 21.4 µg/d and 5% had a folic acid intake above the tolerable upper level of 1000 µg/d [34]. In recent years, several studies have shown that high plasma folate and high folic acid intake, presumably in excess of what is required by the body, can also be associated with negative health outcomes as noted below. High plasma folate and multivitamin use are associated with increased risk for breast cancer in women [35–37]. Among female breast cancer survivors, those who took folic acid supplements or multivitamins but had otherwise poor quality diet was at higher risk for mortality [38]. While adequate folate nutrition is critical for embryonic development, maternal intake of excess folic acid is associated with embryonic developmental disorders in wild type mice and increased incidence of neural tube defects in some mouse models of neural tube defects [39–41]. In a lesion model of central nervous system injury, administration of folic acid resulted in neuronal regeneration, but use of higher concentrations folic acid had a negative influence on neuronal regeneration [42]. Deficiency of folate impairs DNA synthesis and results in anemia [43, 44]. At the other end of the spectrum, presence of unmetabolized folic acid in plasma that is indicative of high folic acid intake is associated with higher incidence of anemia in humans [45], which suggests impairment of DNA synthesis. Telomere length is determined by DNA integrity [6] and if high folic acid intake impairs DNA synthesis it can adversely influence telomere length.

The high plasma folate concentration in Framingham Offspring cohort is the result of high folic acid intake from fortified foods and supplements (Choumenkovich and Selhub, unpublished data). Folic acid fortification appears to have a negative impact on leukocyte telomere length in this cohort, but the effect was not statistically significant. After folic acid fortification, prevalence of individuals who take more than the tolerable upper level for folic acid increased among supplement users in the Framingham Offspring cohort [22]. At the sixth examination of this cohort, 40.7 % of the participants were multivitamin users (Table 1). Multivitamin use was associated with shorter leukocyte telomere length in this study (P=0.015). This result is different from that of Xu et al [25] who showed that multivitamin use is associated with longer telomeres in women. The cohort of Xu et al was comprised of healthy sisters of breast cancer cases [25]. The results of Xu et al might be partially explained by the possibility that the sisters of breast cancer patients who themselves are at a higher risk for cancer development, might adopt a healthier life style (eg: less inclination to smoke) and diet which may also include multivitamin use [25, 46]. A healthy life style and diet are positively associated with telomere length [47, 48]. In Framingham Offspring cohort, multivitamin use was probably not associated with a healthier lifestyle since smoking and alcohol use was not significantly different between multivitamin users and non-users (Online resource 2).

Though the mechanism behind the deleterious effect of excess folic acid intake in humans and animals is not known at present, it has been shown that the enzymes of folate pathway can be inhibited by various folate derivatives [49, 50]. The direction of the metabolic flux in folate pathway is to some extent regulated by concentration of different forms of folate [49, 50]. Folic acid intake in excess of the metabolic capacity of the cell may lead to accumulation of folate derivatives. The enzyme activities thus regulated or inhibited by folate derivatives include, thymidylate synthase, methylene tetrahydrofolate dehydrogenase (MTHFD), 5,10- methenyl tetrahydofolate cyclohydrolase (also carried out by MTHFD) and dihydrofolate reductase [49, 50]. Inhibition of MTHFD, dihydrofolate reductase and thymidylate synthase all contribute to reduced availability of nucleotide precursors and the nucleotide thymidine and thus causing DNA damage, which can potentially result in shorter telomeres. Thus the shorter telomeres in the individuals with high plasma folate concentration could be the result of DNA damage resulting from folic acid intake beyond what is optimal for cellular functions.

The strength of our study includes a community-based cohort that is composed of both men and women, with a wide range of plasma folate concentrations. This cohort also had individuals who were exposed to folic acid fortification and those who were not, allowing us to determine the influence of fortification on leukocyte telomere length. The Framingham Offspring cohort is predominantly Caucasian, and the results of this study may not be applicable to other populations. The median age of this cohort was 54.4 years. We have previously shown that the negative association between the presence of unmetabolized folic acid in plasma and immune function is seen only in older individuals [51]. It is possible effect of excess folic acid intake on telomere length might be different in a younger population.

In conclusion, high plasma folate was associated with shorter leukocyte telomere length. Shortening of telomeres is associated with age-related dysfunctions. While adequate folate nutrition is necessary to maintain DNA integrity and hence that of telomeres, the results of this study suggest that high folate status possibly resulting from high folic acid intake from multivitamins and fortified foods may interfere with the role of folate in maintaining telomere integrity. Additional studies have to be conducted to determine the mechanism behind shortening of telomeres under high folate status and if it is associated with any health outcomes.

Supplementary Material

394_2014_704_MOESM1_ESM

Acknowledgments

Support from United States Department of Agriculture cooperative agreement 51520-008-04S, National Heart Lung and Blood Institute, Framingham Heart Study (NHLBI/NIH Contract #N01-HC-25195) and Boston University School of Medicine. Any opinions, findings, conclusion, or recommendations expressed in this publication are those of the authors and do not necessarily reflect the view of the United States Department of Agriculture.

Footnotes

Conflict of interest

The authors declare that they have no conflict of interest

Contributor Information

Ligi Paul, 711 Washington St, JM USDA HNRC at Tufts University, Boston, MA, 02111.

Paul F. Jacques, 711 Washington St, JM USDA HNRC at Tufts University, Boston, MA, 02111

Abraham Aviv, Center of Human Development and Aging, New Jersey Medical School, Newark, NJ, 07103.

Ramachandran S. Vasan, Framingham Heart Study, National Heart Lung and Blood Institute, Framingham, MA, 01702

Ralph B. D’Agostino, Framingham Heart Study, National Heart Lung and Blood Institute, Framingham, MA, 01702

Daniel Levy, Framingham Heart Study, National Heart Lung and Blood Institute, Framingham, MA, 01702.

Jacob Selhub, 711 Washington St, JM USDA HNRC at Tufts University, Boston, MA, 02111.

References

  • 1.Minamino T, Miyauchi H, Yoshida T, Ishida Y, Yoshida H, Komuro I. Endothelial cell senescence in human atherosclerosis: role of telomere in endothelial dysfunction. Circulation. 2002;105:1541–1544. doi: 10.1161/01.cir.0000013836.85741.17. [DOI] [PubMed] [Google Scholar]
  • 2.Panossian LA, Porter VR, Valenzuela HF, Zhu X, Reback E, Masterman D, Cummings JL, Effros RB. Telomere shortening in T cells correlates with Alzheimer's disease status. Neurobiol Aging. 2003;24:77–84. doi: 10.1016/s0197-4580(02)00043-x. [DOI] [PubMed] [Google Scholar]
  • 3.Guan JZ, Maeda T, Sugano M, Oyama J-i, Higuchi Y, Suzuki T, Makino N. A Percentage Analysis of the Telomere Length in Parkinson's Disease Patients. J Gerontol A Biol Sci Med Sci. 2008;63:467–473. doi: 10.1093/gerona/63.5.467. [DOI] [PubMed] [Google Scholar]
  • 4.Wu X, Amos CI, Zhu Y, Zhao H, Grossman BH, Shay JW, Luo S, Hong WK, Spitz MR. Telomere dysfunction: A potential cancer predisposition factor. J Natl Cancer I. 2003;95:1211–1218. doi: 10.1093/jnci/djg011. [DOI] [PubMed] [Google Scholar]
  • 5.Harley CB, Futcher AB, Greider CW. Telomeres shorten during ageing of human fibroblasts. Nature. 1990;345:458–460. doi: 10.1038/345458a0. [DOI] [PubMed] [Google Scholar]
  • 6.von Zglinicki T, Pilger R, Sitte N. Accumulation of single-strand breaks is the major cause of telomere shortening in human fibroblasts. Free Radic Biol Med. 2000;28:64–74. doi: 10.1016/s0891-5849(99)00207-5. [DOI] [PubMed] [Google Scholar]
  • 7.Benetti R, Gonzalo S, Jaco I, Schotta G, Klatt P, Jenuwein T, Blasco MA. Suv4–20h deficiency results in telomere elongation and derepression of telomere recombination. J Cell Biol. 2007;178:925–936. doi: 10.1083/jcb.200703081. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 8.Garcia-Cao M, O'Sullivan R, Peters AH, Jenuwein T, Blasco MA. Epigenetic regulation of telomere length in mammalian cells by the Suv39h1 and Suv39h2 histone methyltransferases. Nat Genet. 2004;36:94–99. doi: 10.1038/ng1278. [DOI] [PubMed] [Google Scholar]
  • 9.Gonzalo S, Jaco I, Fraga MF, Chen T, Li E, Esteller M, Blasco MA. DNA methyltransferases control telomere length and telomere recombination in mammalian cells. Nat Cell Biol. 2006;8:416–424. doi: 10.1038/ncb1386. [DOI] [PubMed] [Google Scholar]
  • 10.Kruk PA, Rampino NJ, Bohr VA. DNA damage and repair in telomeres: relation to aging. Proc Natl Acad Sci U S A. 1995;92:258–262. doi: 10.1073/pnas.92.1.258. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 11.Latre L, Tusell L, Martin M, Miro R, Egozcue J, Blasco MA, Genesca A. Shortened telomeres join to DNA breaks interfering with their correct repair. Exp Cell Res. 2003;287:282–288. doi: 10.1016/s0014-4827(03)00134-4. [DOI] [PubMed] [Google Scholar]
  • 12.Woods DD. The Function of Folic Acid in Cellular Metabolism. Proc R Soc Med. 1964;57:388–390. doi: 10.1177/003591576405700518. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 13.James SJ, Yin L, Swendseid ME. DNA strand break accumulation, thymidylate synthesis and NAD levels in lymphocytes from methyl donor-deficient rats. J Nutr. 1989;119:661–664. doi: 10.1093/jn/119.4.661. [DOI] [PubMed] [Google Scholar]
  • 14.Paul L, Cattaneo M, D'Angelo A, Sampietro F, Fermo I, Razzari C, Fontana G, Eugene N, Jacques PF, Selhub J. Telomere length in peripheral blood mononuclear cells is associated with folate status in men. J Nutr. 2009;139:1273–1278. doi: 10.3945/jn.109.104984. [DOI] [PubMed] [Google Scholar]
  • 15.Friso S, Choi SW, Girelli D, Mason JB, Dolnikowski GG, Bagley PJ, Olivieri O, Jacques PF, Rosenberg IH, Corrocher R, Selhub J. A common mutation in the 5,10-methylenetetrahydrofolate reductase gene affects genomic DNA methylation through an interaction with folate status. Proc Natl Acad Sci U S A. 2002;99:5606–5611. doi: 10.1073/pnas.062066299. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 16.Bull CF, O'Callaghan NJ, Mayrhofer G, Fenech MF. Telomere length in lymphocytes of older South Australian men may be inversely associated with plasma homocysteine. Rejuvenation Res. 2009;12:341–349. doi: 10.1089/rej.2009.0868. [DOI] [PubMed] [Google Scholar]
  • 17.Richards JB, Valdes AM, Gardner JP, Kato BS, Siva A, Kimura M, Lu X, Brown MJ, Aviv A, Spector TD. Homocysteine levels and leukocyte telomere length. Atherosclerosis. 2008;200:271–277. doi: 10.1016/j.atherosclerosis.2007.12.035. [DOI] [PubMed] [Google Scholar]
  • 18.Jacques PF, Selhub J, Bostom AG, Wilson PW, Rosenberg IH. The effect of folic acid fortification on plasma folate and total homocysteine concentrations. N Engl J Med. 1999;340:1449–1454. doi: 10.1056/NEJM199905133401901. [DOI] [PubMed] [Google Scholar]
  • 19.Feinleib M, Kannel WB, Garrison RJ, McNamara PM, Castelli WP. The Framingham Offspring Study. Design and preliminary data. Prev Med. 1975;4:518–525. doi: 10.1016/0091-7435(75)90037-7. [DOI] [PubMed] [Google Scholar]
  • 20.O'Donnell CJ, Demissie S, Kimura M, Levy D, Gardner JP, White C, D'Agostino RB, Wolf PA, Polak J, Cupples LA, Aviv A. Leukocyte telomere length and carotid artery intimal medial thickness: the Framingham Heart Study. Arterioscler Thromb Vasc Biol. 2008;28:1165–1171. doi: 10.1161/ATVBAHA.107.154849. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 21.Horne DW, Patterson D. Lactobacillus casei microbiological assay of folic acid derivatives in 96-well microtiter plates. Clin Chem. 1988;34:2357–2359. [PubMed] [Google Scholar]
  • 22.Choumenkovitch SF, Selhub J, Wilson PW, Rader JI, Rosenberg IH, Jacques PF. Folic acid intake from fortification in United States exceeds predictions. J Nutr. 2002;132:2792–2798. doi: 10.1093/jn/132.9.2792. [DOI] [PubMed] [Google Scholar]
  • 23.Husdan H, Rapoport A. Estimation of creatinine by the Jaffe reaction. A comparison of three methods. Clin Chem. 1968;14:222–238. [PubMed] [Google Scholar]
  • 24.Shin YS, Rasshofer R, Friedrich B, Endres W. Pyridoxal-5'-phosphate determination by a sensitive micromethod in human blood, urine and tissues; its relation to cystathioninuria in neuroblastoma and biliary atresia. Clin Chim Acta. 1983;127:77–85. doi: 10.1016/0009-8981(83)90077-3. [DOI] [PubMed] [Google Scholar]
  • 25.Xu Q, Parks CG, DeRoo LA, Cawthon RM, Sandler DP, Chen H. Multivitamin use and telomere length in women. Am J Clin Nutr. 2009;89:1857–1863. doi: 10.3945/ajcn.2008.26986. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 26.Liu JJ, Prescott J, Giovannucci E, Hankinson SE, Rosner B, De Vivo I. One-carbon metabolism factors and leukocyte telomere length. Am J Clin Nutr. 2013;97:794–799. doi: 10.3945/ajcn.112.051557. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 27.Codd V, Mangino M, van der Harst P, Braund PS, Kaiser M, Beveridge AJ, Rafelt S, Moore J, Nelson C, Soranzo N, Zhai G, Valdes AM, Blackburn H, Leach IM, de Boer RA, Kimura M, Aviv A, Consortium WTCC, Goodall AH, Ouwehand W, van Veldhuisen DJ, van Gilst WH, Navis G, Burton PR, Tobin MD, Hall AS, Thompson JR, Spector T, Samani NJ. Common variants near TERC are associated with mean telomere length. Nat Genet. 2010;42:197–199. doi: 10.1038/ng.532. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 28.Bleys J, Navas-Acien A, Guallar E. Serum selenium levels and all-cause, cancer, and cardiovascular mortality among us adults. Arch Intern Med. 2008;168:404–410. doi: 10.1001/archinternmed.2007.74. [DOI] [PubMed] [Google Scholar]
  • 29.Gibson T, Weinstein S, Mayne S, Pfeiffer R, Selhub J, Taylor P, Virtamo J, Albanes D, Stolzenberg-Solomon R. A prospective study of one-carbon metabolism biomarkers and risk of renal cell carcinoma. Cancer Cause Control. 2010;21:1061–1069. doi: 10.1007/s10552-010-9534-5. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 30.Zhang SM, Willett WC, Selhub J, Hunter DJ, Giovannucci EL, Holmes MD, Colditz GA, Hankinson SE. Plasma folate, vitamin B6, vitamin B12, homocysteine, and risk of breast cancer. J Natl Cancer I. 2003;95:373–380. doi: 10.1093/jnci/95.5.373. [DOI] [PubMed] [Google Scholar]
  • 31.Morrison HI, Schaubel D, Desmeules M, Wigle DT. Serum folate and risk of fatal coronary heart disease. JAMA. 1996;275:1893–1896. doi: 10.1001/jama.1996.03530480035037. [DOI] [PubMed] [Google Scholar]
  • 32.Wang H, Odegaard A, Thyagarajan B, Hayes J, Cruz KS, Derosiers MF, Tyas SL, Gross MD. Blood folate is associated with asymptomatic or partially symptomatic Alzheimer's disease in the Nun study. J Alzheimer dis. 2012;28:637–645. doi: 10.3233/JAD-2011-111271. [DOI] [PubMed] [Google Scholar]
  • 33.Smithells RW, Sheppard S, Schorah CJ, Seller MJ, Nevin NC, Harris R, Read AP, Fielding DW. Possible prevention of neural-tube defects by periconceptional vitamin supplementation. Lancet. 1980;1:339–340. doi: 10.1016/s0140-6736(80)90886-7. [DOI] [PubMed] [Google Scholar]
  • 34.Bailey RL, Dodd KW, Gahche JJ, Dwyer JT, McDowell MA, Yetley EA, Sempos CA, Burt VL, Radimer KL, Picciano MF. Total folate and folic acid intake from foods and dietary supplements in the United States, 2003–2006. Am J Clin Nutr. 2010;91:231–237. doi: 10.3945/ajcn.2009.28427. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 35.Hara A, Sasazuki S, Inoue M, Shimazu T, Iwasaki M, Sawada N, Yamaji T, Ishihara J, Iso H, Tsugane S. Use of vitamin supplements and risk of total cancer and cardiovascular disease among the Japanese general population: a population-based survey. BMC Public Health. 2011;11:540. doi: 10.1186/1471-2458-11-540. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 36.Larsson SC, Akesson A, Bergkvist L, Wolk A. Multivitamin use and breast cancer incidence in a prospective cohort of Swedish women. Am J Clin Nutr. 2010;91:1268–1272. doi: 10.3945/ajcn.2009.28837. [DOI] [PubMed] [Google Scholar]
  • 37.Ericson U, Borgquist S, Ivarsson MIL, Sonestedt E, Gullberg B, Carlson J, Olsson H, Jirstram K, Wirfolt E. Plasma folate concentrations are positively associated with risk of estrogen β receptor negative breast cancer in a swedish nested case control study. J Nutr. 2010;140:1661–1668. doi: 10.3945/jn.110.124313. [DOI] [PubMed] [Google Scholar]
  • 38.Inoue-Choi M, Greenlee H, Oppeneer SJ, Robien K. The association between postdiagnosis dietary supplement use and total mortality differs by diet quality among older female cancer survivors. Cancer Epidem Biomar. 2014 doi: 10.1158/1055-9965.EPI-13-1303. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 39.Pickell L, Brown K, Li D, Wang XL, Deng L, Wu Q, Selhub J, Luo L, Jerome-Majewska L, Rozen R. High intake of folic acid disrupts embryonic development in mice. Birth Defects Res A Clin Mol Teratol. 2010;91:8–19. doi: 10.1002/bdra.20754. [DOI] [PubMed] [Google Scholar]
  • 40.Marean A, Graf A, Zhang Y, Niswander L. Folic acid supplementation can adversely affect murine neural tube closure and embryonic survival. Hum Mol Genet. 2011;20:3678–3683. doi: 10.1093/hmg/ddr289. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 41.Mikael LG, Deng L, Paul L, Selhub J, Rozen R. Moderately high intake of folic acid has a negative impact on mouse embryonic development. Birth Defects Res A Clin Mol Teratol. 2013;97:47–52. doi: 10.1002/bdra.23092. [DOI] [PubMed] [Google Scholar]
  • 42.Iskandar BJ, Nelson A, Resnick D, Skene JH, Gao P, Johnson C, Cook TD, Hariharan N. Folic acid supplementation enhances repair of the adult central nervous system. Ann Neurol. 2004;56:221–227. doi: 10.1002/ana.20174. [DOI] [PubMed] [Google Scholar]
  • 43.Wills L, Clutterbuck PW, Evans BD. A new factor in the production and cure of macrocytic anaemias and its relation to other haemopoietic principles curative in pernicious anaemia. Biochem J. 1937;31:2136–2147. doi: 10.1042/bj0312136. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 44.Thomas ED, Lochte HL., Jr Studies on the biochemical defect of pernicious anemia. I. In vitro observations on oxygen consumption, heme synthesis and deoxyribonucleic acid synthesis by pernicious anemia bone marrow. J Clin Invest. 1958;37:166–171. doi: 10.1172/JCI103595. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 45.Morris MS, Jacques PF, Rosenberg IH, Selhub J. Circulating unmetabolized folic acid and 5-methyltetrahydrofolate in relation to anemia, macrocytosis, and cognitive test performance in American seniors. Am J Clin Nutr. 2010;91:1733–1744. doi: 10.3945/ajcn.2009.28671. [DOI] [PubMed] [Google Scholar]
  • 46.Aviv A. Leukocyte telomere length: the telomere tale continues. Am J Clin Nutr. 2009;89:1721–1722. doi: 10.3945/ajcn.2009.27807. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 47.Mirabello L, Huang W-Y, Wong JYY, Chatterjee N, Reding D, David Crawford E, De Vivo I, Hayes RB, Savage SA. The association between leukocyte telomere length and cigarette smoking, dietary and physical variables, and risk of prostate cancer. Aging Cell. 2009;8:405–413. doi: 10.1111/j.1474-9726.2009.00485.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 48.Paul L. Diet, nutrition and telomere length. The Journal of nutritional biochemistry. 2011;22:895–901. doi: 10.1016/j.jnutbio.2010.12.001. [DOI] [PubMed] [Google Scholar]
  • 49.Rowe PB, Lewis GP. Mammalian folate metabolism. Regulation of folate interconversion enzymes. Biochemistry. 1973;12:1862–1869. doi: 10.1021/bi00734a020. [DOI] [PubMed] [Google Scholar]
  • 50.Matthews RG, Ghose C, Green JM, Matthews KD, Dunlap RB. Folylpolyglutamates as substrates and inhibitors of folate-dependent enzymes. Adv Enzyme Regul. 1987;26:157–171. doi: 10.1016/0065-2571(87)90012-4. [DOI] [PubMed] [Google Scholar]
  • 51.Troen AM, Mitchell B, Sorensen B, Wener MH, Johnston A, Wood B, Selhub J, McTiernan A, Yasui Y, Oral E, Potter JD, Ulrich CM. Unmetabolized folic acid in plasma is associated with reduced natural killer cell cytotoxicity among postmenopausal women. J Nutr. 2006;136:189–194. doi: 10.1093/jn/136.1.189. [DOI] [PubMed] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

394_2014_704_MOESM1_ESM
NIHMS592112-supplement-394_2014_704_MOESM1_ESM.docx (20.5KB, docx)

RESOURCES