Supplement concerns—an appeal to nature

I’ve become increasingly concerned about the efficacy and safety of some typical nutritional supplements—here’s why.

Initially, my concern is a logical appeal to nature. Food contains a complex matrix of chemicals in the balance and structure of life, to which our physiology (e.g. digestion, metabolism and microbiome) is adapted. By comparison, supplements supply concentrated food ingredients, to an extreme of isolated chemicals in unnatural forms and mega doses. My concern is fed by some studies reporting on potentially negative effects and long-term health outcomes (see table); common themes are the use of synthetic/isolated nutrients and high doses (note their use also in ME/CFS studies ^1–5). Could these deviations from nature impair bioactivity or induce imbalances which limit efficacy and introduce risk? Some specific examples are discussed below.

Quality

Firstly, supplement quality regulation is variable, so products can have varied levels of active ingredients and contaminants ⁶ (e.g. toxic metals ^7,8). In addition, some isolated ingredients and combinations may be prone to oxidation. For instance, fish oils are one of the most labile supplements. Studies in different countries have reported that many commercial fish oils are high in oxidation products, exceeding recommended limits for standards of quality ⁹. Further oxidation might also occur in the stomach, as reported in gastric models ^10,11. This may affect bioactivity. In vitro, commercial oxidised fish oils had impaired ability to inhibit oxidation of LDL cholesterol ¹², while a clinical trial showed opposite effects on IDL/LDL composition and level ¹³. Similarly, multi-vit/min supplements containing redox-active transition metals (e.g. inorganic iron and copper) and vitamins (e.g. vit-C/E) can form free radicals and oxidise in water and gut (mouse model), likely due to Fenton reactions ¹⁴. Typical supplements also contain synthetic vitamins, which can be more stable, but potentially less bioactive. For instance, folic acid (vit-B₉) and cyanocobalamin (vit-B₁₂), despite raising blood levels, may be less efficiently converted to active forms in tissues ^15–17.

Quantity

Besides quality issues, excessive doses might also be disruptive to cell metabolism and signalling. For instance, some nutrients are metabolised via methylation. Consequently, high-dose niacinamide (NAM, vit-B₃) can acutely deplete betaine, elevate homocysteine and lower methylation reactions in humans ¹⁸ (more than NA ¹⁹). Fat-soluble vitamins and carotenoids can also compete for absorption ^20–22, while unabsorbed doses may accumulate in gut cells ²³. Consequently, while vit-E exists as 8 forms in nature (4 tocopherols and tocotrienols), typical alpha-tocopherol (aT) supplementation lowers b, g and dT in humans (i.e. RRR-aT ^24,25 and all-rac-aT ²⁶), and potentially tocotrienols ²⁷, all of which may have unique benefits (e.g. anti-cancer activity ²⁸). Further, antioxidants and oxidants function within complex redox networks, organised in space and time to control basic cellular processes ²⁹, suggesting potential to dysregulate redox biology. For instance, high doses of antioxidants (e.g. vit-C + aT) can inhibit exercise-induced redox signalling ^30–32 and favourable adaptations (e.g. insulin sensitivity, performance) in some animal and human trials ^33–35. Excessive antioxidant supplementation might also indiscriminately support pathogenic cells (e.g. cancerous), as shown in animal models ^36–38.

Supplements might also inadvertently affect the gut microbiome, which responds rapidly to changes in diet ³⁹ and redox ⁴⁰, and influences systemic health. For instance, microbial metabolism of TMA-containing nutrients (e.g. choline and carnitine ⁴¹) can fuel production of TMAO, via a meta-organismal pathway (i.e. TMA–FMO3–TMAO) associated with age-related diseases (e.g. CVD, dementia, etc.) ^42–44. Consequently, high-dose choline ⁴⁵ and carnitine ⁴⁶ supplements can greatly elevate TMAO (>10-fold) and alter platelet function in humans ⁴⁵. B₁₂ is also often taken at extremely high doses (e.g. supplements 1mg+, diets 5–10ug ⁴⁷) with limited absorption (via active transport and passive diffusion), meaning most will pass through the gut. B₁₂ is normally a limited resource for gut microbes ⁴⁸, while recent preclinical studies show an ability of cyanocobalamin in particular to unfavourably modulate the colonic microbiome ⁴⁹ and exacerbate IBD in mice ⁵⁰.

Context

On the other hand, too little of any particular nutrient/metabolite is also potentially detrimental, and may occur for various reasons. Diet is the natural source of nutrients, though perhaps not always optimal ⁵¹. Common refined ingredients (e.g. sugar, refined grains, oil/butter and protein isolates) provide empty calories (macros), depleted in micro- and phytonutrients. Even whole foods can have altered nutrient/toxin content due to industrialisation (e.g. crops ^52,53 and seafood ^54,55). Moreover, metabolism is affected by genetics, diseases, ageing, etc. So appropriate supplementation might be supportive, but when overly crude might induce its own issues; i.e. too little or too much might be harmful—exact margins depending on individual context ⁵⁶.

This may introduce further confounding into RCTs to obscure and confuse outcomes. For instance, while the recent large VITAL trial with prescription omega-3 did not prevent CVD (or cancer) ⁵⁷, subgroup analysis showed marked benefit in those with low fish intake ⁵⁸. A meta-analysis of CVD trials with B-vitamins linked high-dose cyanocobalamin to harm in people with impaired renal function, obscuring benefit in those with good function ⁵⁹. Further, the VITACOG trial of B-vitamins in MCI slowed cognitive decline and brain atrophy, but only in those with elevated baseline homocysteine ^60,61 and omega-3 ^62,63, suggesting metabolic interdependence (as discussed previously). A meta-analysis of vit-D trials reported that daily/weekly doses, but not bolus, prevented respiratory infections, and most prominently in those with low baseline status ⁶⁴. In people with low antioxidant status (i.e. vit-C and GSH), supplementation has improved exercise redox and performance ^65–67, while excessive doses may be detrimental in healthy individuals (as above). In observational studies, higher intake and blood levels of various antioxidants are associated with reduced mortality ^68,69, whereas in some trials and meta-analyses, typical antioxidant supplementation even increased cancer (e.g. SELECT) or mortality (for review ⁷⁰), again in relation to dose (e.g. vit-E and β-carotene >RDA) ⁵⁶ and baseline selenium levels ⁷¹.

In sum, the effects of supplements can depend upon their quality, quantity and context, all of which may be confounding factors in trials, leading to inconsistent results and misalignment with other lines of evidence (e.g. epidemiology and models). In particular, nutrients are often treated like foreign drugs with linear effects, yet they are already present in natural forms and function within metabolic networks with complex dynamics ⁷². Perhaps appreciating these nuances or adhering closer to nature could support efficacy and safety?

Resources

• Cronometer (nutrient tracker)
• Antioxidant content of foods
• Labdoor (supplement analysis)

References

1.           Brouwers, F. M., Van Der Werf, S., Bleijenberg, G., Van Der Zee, L. & Van Der Meer, J. W. M. The effect of a polynutrient supplement on fatigue and physical activity of patients with chronic fatigue syndrome: a double-blind randomized controlled trial. QJM 95, 677–683 (2002).

2.           Menon, R. et al. Mitochondrial modifying nutrients in treating chronic fatigue syndrome: A 16-week open-label pilot study. Adv. Integr. Med. 4, 109–114 (2017).

3.           Martin, R. W. Y., Ogston, S. A. & Evans, J. R. Effects of Vitamin and Mineral Supplementation on Symptoms Associated with Chronic Fatigue Syndrome with Coxsackie B Antibodies. J. Nutr. Med. 4, 11–23 (1994).

4.           Montoya, J. G. et al. KPAX002 as a treatment for Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS): a prospective, randomized trial. Int. J. Clin. Exp. Med. 11, 2890–2900 (2018).

5.           Regland, B. et al. Response to Vitamin B12 and Folic Acid in Myalgic Encephalomyelitis and Fibromyalgia. PLoS One 10, e0124648 (2015).

6.           Costa, J. G. et al. Contaminants: a dark side of food supplements? Free Radic. Res. 0, 1–23 (2019).

7.           Schwalfenberg, G., Rodushkin, I. & Genuis, S. J. Heavy metal contamination of prenatal vitamins. Toxicol. reports 5, 390–395 (2018).

8.           Genuis, S. J., Schwalfenberg, G., Siy, A.-K. J. & Rodushkin, I. Toxic element contamination of natural health products and pharmaceutical preparations. PLoS One 7, e49676 (2012).

9.           Cameron-Smith, D., Albert, B. B. & Cutfield, W. S. Fishing for answers: is oxidation of fish oil supplements a problem? J. Nutr. Sci. 4, e36 (2015).

10.        Tirosh, O., Shpaizer, A. & Kanner, J. Lipid Peroxidation in a Stomach Medium Is Affected by Dietary Oils (Olive/Fish) and Antioxidants: The Mediterranean versus Western Diet. J. Agric. Food Chem. 63, 7016–23 (2015).

11.        Kanner, J. et al. Redox homeostasis in stomach medium by foods: The Postprandial Oxidative Stress Index (POSI) for balancing nutrition and human health. Redox Biol. 12, 929–936 (2017).

12.        Mason, R. P. & Sherratt, S. C. R. Omega-3 fatty acid fish oil dietary supplements contain saturated fats and oxidized lipids that may interfere with their intended biological benefits. Biochem. Biophys. Res. Commun. 483, 425–429 (2017).

13.        Rundblad, A., Holven, K. B., Ottestad, I., Myhrstad, M. C. & Ulven, S. M. High-quality fish oil has a more favourable effect than oxidised fish oil on intermediate-density lipoprotein and LDL subclasses: a randomised controlled trial. Br. J. Nutr. 117, 1291–1298 (2017).

14.        Rabovsky, A. B., Buettner, G. R. & Fink, B. In vivo imaging of free radicals produced by multivitamin-mineral supplements. BMC Nutr. 1, 1–9 (2015).

15.        Scaglione, F. & Panzavolta, G. Folate, folic acid and 5-methyltetrahydrofolate are not the same thing. Xenobiotica. 44, 480–8 (2014).

16.        Hall, C., Begley, J. & Green-Colligan, P. The availability of therapeutic hydroxocobalamin to cells. Blood 63, 335–341 (1984).

17.        Greibe, E. et al. The tissue profile of metabolically active coenzyme forms of vitamin B12 differs in vitamin B12-depleted rats treated with hydroxo-B12 or cyano-B12. Br. J. Nutr. 120, 49–56 (2018).

18.        Sun, W.-P. et al. Excess nicotinamide inhibits methylation-mediated degradation of catecholamines in normotensives and hypertensives. Hypertens. Res. 35, 180–5 (2012).

19.        Sun, W.-P. et al. Comparison of the effects of nicotinic acid and nicotinamide degradation on plasma betaine and choline levels. Clin. Nutr. 36, 1136–1142 (2017).

20.        Reboul, E. et al. Effect of the main dietary antioxidants (carotenoids, gamma-tocopherol, polyphenols, and vitamin C) on alpha-tocopherol absorption. Eur. J. Clin. Nutr. 61, 1167–73 (2007).

21.        Reboul, E. et al. Differential effect of dietary antioxidant classes (carotenoids, polyphenols, vitamins C and E) on lutein absorption. Br. J. Nutr. 97, 440–6 (2007).

22.        Reboul, E. Vitamin e bioavailability: Mechanisms of intestinal absorption in the spotlight. Antioxidants 6, (2017).

23.        Reboul, E. The gut: a regulatory hall governing fat-soluble micronutrient absorption. Am. J. Clin. Nutr. (2019). doi:10.1093/ajcn/nqz199

24.        Gutierrez, A. D., de Serna, D. G., Robinson, I. & Schade, D. S. The response of gamma vitamin E to varying dosages of alpha vitamin E plus vitamin C. Metabolism. 58, 469–78 (2009).

25.        Huang, H.-Y. & Appel, L. J. Supplementation of diets with alpha-tocopherol reduces serum concentrations of gamma- and delta-tocopherol in humans. J. Nutr. 133, 3137–40 (2003).

26.        Mondul, A. M. et al. Serum Metabolomic Response to Long-Term Supplementation with all-rac-α-Tocopheryl Acetate in a Randomized Controlled Trial. J. Nutr. Metab. 2016, 6158436 (2016).

27.        Gee, P. T. Unleashing the untold and misunderstood observations on vitamin E. Genes Nutr. 6, 5–16 (2011).

28.        Jiang, Q. Natural Forms of Vitamin E as Effective Agents for Cancer Prevention and Therapy. Adv. Nutr. 8, 850–867 (2017).

29.        Jones, D. P. & Sies, H. The Redox Code. Antioxid. Redox Signal. 23, 734–46 (2015).

30.        Done, A. J. & Traustadóttir, T. Nrf2 mediates redox adaptations to exercise. Redox Biol. 10, 191–199 (2016).

31.        Ristow, M. & Schmeisser, K. Mitohormesis: Promoting Health and Lifespan by Increased Levels of Reactive Oxygen Species (ROS). Dose. Response. 12, 288–341 (2014).

32.        Merry, T. L. & Ristow, M. Nuclear factor erythroid-derived 2-like 2 (NFE2L2, Nrf2) mediates exercise-induced mitochondrial biogenesis and the anti-oxidant response in mice. J. Physiol. 594, 5195–207 (2016).

33.        Nikolaidis, M. G., Kerksick, C. M., Lamprecht, M. & McAnulty, S. R. Does vitamin C and E supplementation impair the favorable adaptations of regular exercise? Oxid. Med. Cell. Longev. 2012, 707941 (2012).

34.        Merry, T. L. & Ristow, M. Do antioxidant supplements interfere with skeletal muscle adaptation to exercise training? J. Physiol. 594, 5135–47 (2016).

35.        Gomez-Cabrera, M. C., Salvador-Pascual, A., Cabo, H., Ferrando, B. & Vina, J. Redox modulation of mitochondriogenesis in exercise. Does antioxidant supplementation blunt the benefits of exercise training? Free Radic. Biol. Med. 86, 37–46 (2015).

36.        Cockfield, J. A. & Schafer, Z. T. Antioxidant Defenses: A Context-Specific Vulnerability of Cancer Cells. Cancers (Basel). 11, 1208 (2019).

37.        Sayin, V. I. et al. Antioxidants accelerate lung cancer progression in mice. Sci. Transl. Med. 6, 221ra15 (2014).

38.        Le Gal, K. et al. Antioxidants can increase melanoma metastasis in mice. Sci. Transl. Med. 7, 308re8 (2015).

39.        David, L. a et al. Diet rapidly and reproducibly alters the human gut microbiome. Nature 505, 559–63 (2014).

40.        Rivera-Chávez, F., Lopez, C. A. & Bäumler, A. J. Oxygen as a driver of gut dysbiosis. Free Radic. Biol. Med. 105, 93–101 (2017).

41.        Li, X. S. et al. Untargeted metabolomics identifies trimethyllysine, a TMAO-producing nutrient precursor, as a predictor of incident cardiovascular disease risk. JCI insight 3, 1–18 (2018).

42.        Vogt, N. M. et al. The gut microbiota-derived metabolite trimethylamine N -oxide is elevated in Alzheimer’s disease. Alzheimer’s Res. Ther. 2018 101 10, 124 (2018).

43.        Brunt, V. E. et al. Trimethylamine-N-Oxide Promotes Age-Related Vascular Oxidative Stress and Endothelial Dysfunction in Mice and Healthy Humans. Hypertension 76, 101–112 (2020).

44.        Randrianarisoa, E. et al. Relationship of Serum Trimethylamine N-Oxide (TMAO) Levels with early Atherosclerosis in Humans. Sci. Rep. 6, 26745 (2016).

45.        Zhu, W., Wang, Z., Tang, W. H. W. & Hazen, S. L. Gut Microbe-Generated Trimethylamine N-Oxide From Dietary Choline Is Prothrombotic in Subjects. Circulation 135, 1671–1673 (2017).

46.        Vallance, H. D. et al. Marked elevation in plasma trimethylamine-N-oxide (TMAO) in patients with mitochondrial disorders treated with oral l-carnitine. Mol. Genet. Metab. reports 15, 130–133 (2018).

47.        Kraft, T. S. et al. Nutrition transition in 2 lowland Bolivian subsistence populations. Am. J. Clin. Nutr. 108, 1183–1195 (2018).

48.        Rowley, C. A. & Kendall, M. M. To B12 or not to B12: Five questions on the role of cobalamin in host-microbial interactions. PLoS Pathog. 15, e1007479 (2019).

49.        Xu, Y. et al. Cobalamin (Vitamin B12) Induced a Shift in Microbial Composition and Metabolic Activity in an in vitro Colon Simulation. Front. Microbiol. 9, 2780 (2018).

50.        Zhu, X. et al. Impact of Cyanocobalamin and Methylcobalamin on Inflammatory Bowel Disease and the Intestinal Microbiota Composition. J. Agric. Food Chem. 67, 916–926 (2019).

51.        Kennedy, D. O. et al. Multivitamins and minerals modulate whole-body energy metabolism and cerebral blood-flow during cognitive task performance: a double-blind, randomised, placebo-controlled trial. Nutr. Metab. (Lond). 13, 11 (2016).

52.        Barański, M. et al. Higher antioxidant and lower cadmium concentrations and lower incidence of pesticide residues in organically grown crops: a systematic literature review and meta-analyses. Br. J. Nutr. 112, 1–18 (2014).

53.        Crinnion, W. J. Organic Foods Contain Higher Levels of Certain Nutrients, Lower Levels of Pesticides, and May Provide Health Benefits for the Consumer. Altern. Med. Rev. 15, (2010).

54.        Shi, L. et al. Joint Analysis of Metabolite Markers of Fish Intake and Persistent Organic Pollutants in Relation to Type 2 Diabetes Risk in Swedish Adults. J. Nutr. 149, 1413–1423 (2019).

55.        Donat-Vargas, C. et al. Cardiovascular and cancer mortality in relation to dietary polychlorinated biphenyls and marine polyunsaturated fatty acids: a nutritional-toxicological aspect of fish consumption. J. Intern. Med. 287, 197–209 (2020).

56.        Bjelakovic, G., Nikolova, D. & Gluud, C. Meta-regression analyses, meta-analyses, and trial sequential analyses of the effects of supplementation with beta-carotene, vitamin A, and vitamin E singly or in different combinations on all-cause mortality: do we have evidence for lack of harm? PLoS One 8, e74558 (2013).

57.        Manson, J. E. et al. Marine n-3 Fatty Acids and Prevention of Cardiovascular Disease and Cancer. N. Engl. J. Med. 380, 23–32 (2019).

58.        Kris-Etherton, P. M. et al. Recent Clinical Trials Shed New Light on the Cardiovascular Benefits of Omega-3 Fatty Acids. Methodist Debakey Cardiovasc. J. 15, 171–178 (2019).

59.        Spence, J. D., Yi, Q. & Hankey, G. J. B vitamins in stroke prevention: time to reconsider. Lancet Neurol. 16, 750–760 (2017).

60.        Douaud, G. et al. Preventing Alzheimer’s disease-related gray matter atrophy by B-vitamin treatment. Proc. Natl. Acad. Sci. 110, 9523–8 (2013).

61.        de Jager, C. A., Oulhaj, A., Jacoby, R., Refsum, H. & Smith, A. D. Cognitive and clinical outcomes of homocysteine-lowering B-vitamin treatment in mild cognitive impairment: a randomized controlled trial. Int. J. Geriatr. Psychiatry 27, 592–600 (2012).

62.        Oulhaj, A., Jernerén, F., Refsum, H., Smith, A. D. & de Jager, C. A. Omega-3 Fatty Acid Status Enhances the Prevention of Cognitive Decline by B Vitamins in Mild Cognitive Impairment. J. Alzheimers. Dis. 50, 547–57 (2016).

63.        Jerneren, F. et al. Brain atrophy in cognitively impaired elderly: the importance of long-chain -3 fatty acids and B vitamin status in a randomized controlled trial. Am. J. Clin. Nutr. 102, 215–21 (2015).

64.        Martineau, A. R. et al. Vitamin D supplementation to prevent acute respiratory tract infections: Systematic review and meta-analysis of individual participant data. BMJ 356, (2017).

65.        Paschalis, V., Theodorou, A. A., Margaritelis, N. V, Kyparos, A. & Nikolaidis, M. G. N-acetylcysteine supplementation increases exercise performance and reduces oxidative stress only in individuals with low levels of glutathione. Free Radic. Biol. Med. 115, 288–297 (2018).

66.        Johnston, C. S., Corte, C. & Swan, P. D. Marginal vitamin C status is associated with reduced fat oxidation during submaximal exercise in young adults. Nutr. Metab. (Lond). 3, 35 (2006).

67.        Paschalis, V. et al. Low vitamin C values are linked with decreased physical performance and increased oxidative stress: reversal by vitamin C supplementation. Eur. J. Nutr. 55, 45–53 (2016).

68.        Jayedi, A., Rashidy-Pour, A., Parohan, M., Zargar, M. S. & Shab-Bidar, S. Dietary Antioxidants, Circulating Antioxidant Concentrations, Total Antioxidant Capacity, and Risk of All-Cause Mortality: A Systematic Review and Dose-Response Meta-Analysis of Prospective Observational Studies. Adv. Nutr. 9, 701–716 (2018).

69.        Parohan, M. et al. Dietary total antioxidant capacity and mortality from all causes, cardiovascular disease and cancer: a systematic review and dose-response meta-analysis of prospective cohort studies. Eur. J. Nutr. 58, 2175–2189 (2019).

70.        Bjelakovic, G., Nikolova, D. & Gluud, C. Antioxidant supplements and mortality. Curr. Opin. Clin. Nutr. Metab. Care 17, 40–4 (2014).

71.        Kristal, A. R. et al. Baseline selenium status and effects of selenium and vitamin e supplementation on prostate cancer risk. J. Natl. Cancer Inst. 106, djt456 (2014).

72.        Grant, W. B., Boucher, B. J., Bhattoa, H. P. & Lahore, H. Why vitamin D clinical trials should be based on 25-hydroxyvitamin D concentrations. J. Steroid Biochem. Mol. Biol. 177, 266–269 (2018).

73.        Jenkins, D. J. A. et al. Supplemental Vitamins and Minerals for CVD Prevention and Treatment. Journal of the American College of Cardiology 71, 2570–2584 (2018).

74.        Ohkawa, S. et al. Pro-oxidative effect of alpha-tocopherol in the oxidation of LDL isolated from co-antioxidant-depleted non-diabetic hemodialysis patients. Atherosclerosis 176, 411–8 (2004).

75.        Pearson, P., Lewis, S. A., Britton, J., Young, I. S. & Fogarty, A. The pro-oxidant activity of high-dose vitamin E supplements in vivo. BioDrugs 20, 271–3 (2006).

76.        Poulsen, H. E. et al. Does vitamin C have a pro-oxidant effect? Nature 395, 231–232 (1998).

77.        Cha, J.-H., Yu, Q.-M. & Seo, J.-S. Vitamin A supplementation modifies the antioxidant system in rats. Nutr. Res. Pract. 10, 26–32 (2016).

78.        Underwood, B. R. et al. Antioxidants can inhibit basal autophagy and enhance neurodegeneration in models of polyglutamine disease. Hum. Mol. Genet. 19, 3413–29 (2010).

79.        Woodside, J. V et al. Effect of B-group vitamins and antioxidant vitamins on hyperhomocysteinemia: a double-blind, randomized, factorial-design, controlled trial. Am. J. Clin. Nutr. 67, 858–66 (1998).

80.        Cafolla, A. et al. Effect of folic acid and vitamin C supplementation on folate status and homocysteine level: a randomised controlled trial in Italian smoker-blood donors. Atherosclerosis 163, 105–11 (2002).

81.        Ullegaddi, R., Powers, H. J. & Gariballa, S. E. Antioxidant supplementation with or without B-group vitamins after acute ischemic stroke: a randomized controlled trial. JPEN. J. Parenter. Enteral Nutr. 30, 108–14 (2006).

82.        Schwarz, N. A. et al. (-)-Epicatechin Supplementation Inhibits Aerobic Adaptations to Cycling Exercise in Humans. Front. Nutr. 5, 132 (2018).

83.        Gliemann, L., Nyberg, M. & Hellsten, Y. Effects of exercise training and resveratrol on vascular health in aging. Free Radic. Biol. Med. 98, 165–176 (2016).

84.        Stabler, S. P., Sekhar, J., Allen, R. H., O’Neill, H. C. & White, C. W. Alpha-lipoic acid induces elevated S-adenosylhomocysteine and depletes S-adenosylmethionine. Free Radic. Biol. Med. 47, 1147–53 (2009).

85.        Hwang, E. S. & Song, S. B. Nicotinamide is an inhibitor of SIRT1 in vitro, but can be a stimulator in cells. Cell. Mol. Life Sci. 74, 3347–3362 (2017).

86.        Conze, D., Brenner, C. & Kruger, C. L. Safety and Metabolism of Long-term Administration of NIAGEN (Nicotinamide Riboside Chloride) in a Randomized, Double-Blind, Placebo-controlled Clinical Trial of Healthy Overweight Adults. Sci. Rep. 9, 9772 (2019).

87.        Kourtzidis, I. A. et al. Nicotinamide riboside supplementation dysregulates redox and energy metabolism in rats: Implications for exercise performance. Exp. Physiol. 103, 1357–1366 (2018).

88.        Suidasari, S., Uragami, S., Yanaka, N. & Kato, N. Dietary vitamin B6 modulates the gene expression of myokines, Nrf2-related factors, myogenin and HSP60 in the skeletal muscle of rats. Exp. Ther. Med. 14, 3239–3246 (2017).

89.        Kim, Y. I. Folate and cancer: A tale of Dr. Jekyll and Mr. Hyde? Am. J. Clin. Nutr. 107, 139–142 (2018).

90.        Brasky, T. M., White, E. & Chen, C.-L. Long-Term, Supplemental, One-Carbon Metabolism-Related Vitamin B Use in Relation to Lung Cancer Risk in the Vitamins and Lifestyle (VITAL) Cohort. J. Clin. Oncol. 35, 3440–3448 (2017).

91.        Spence, J. D. Harm With High Levels of Serum B12 in Elderly Persons. J. Gerontol. A. Biol. Sci. Med. Sci. 74, 137 (2019).

92.        Bailey, S. W. & Ayling, J. E. The extremely slow and variable activity of dihydrofolate reductase in human liver and its implications for high folic acid intake. Proc. Natl. Acad. Sci. U. S. A. 106, 15424–9 (2009).

93.        Patanwala, I. et al. Folic acid handling by the human gut: implications for food fortification and supplementation. Am. J. Clin. Nutr. 100, 593–9 (2014).

94.        Smith, D. E. C., Hornstra, J. M., Kok, R. M., Blom, H. J. & Smulders, Y. M. Folic acid supplementation does not reduce intracellular homocysteine, and may disturb intracellular one-carbon metabolism. Clin. Chem. Lab. Med. 51, 1643–50 (2013).

95.        Smith, D. et al. Folic Acid Impairs the Uptake of 5-Methyltetrahydrofolate in Human Umbilical Vascular Endothelial Cells. J. Cardiovasc. Pharmacol. 70, 271–275 (2017).

96.        Paniz, C. et al. A Daily Dose of 5 mg Folic Acid for 90 Days Is Associated with Increased Serum Unmetabolized Folic Acid and Reduced Natural Killer Cell Cytotoxicity in Healthy Brazilian Adults. J. Nutr. 147, 1677–1685 (2017).

97.        Offer, T. et al. 5-Methyltetrahydrofolate inhibits photosensitization reactions and strand breaks in DNA. FASEB J. 21, 2101–7 (2007).

98.        Kelly, C. J. et al. Oral vitamin B12 supplement is delivered to the distal gut, altering the corrinoid profile and selectively depleting Bacteroides in C57BL/6 mice. Gut Microbes 10, 654–662 (2019).

99.        Bergström, T., Ersson, C., Bergman, J. & Möller, L. Vitamins at physiological levels cause oxidation to the DNA nucleoside deoxyguanosine and to DNA--alone or in synergism with metals. Mutagenesis 27, 511–7 (2012).

100.      Mahalhal, A. et al. Oral iron exacerbates colitis and influences the intestinal microbiome. PLoS One 13, e0202460 (2018).

101.      Li, S. et al. Long-term calcium supplementation may have adverse effects on serum cholesterol and carotid intima-media thickness in postmenopausal women: a double-blind, randomized, placebo-controlled trial. Am. J. Clin. Nutr. 98, 1353–9 (2013).

102.      Tankeu, A. T., Ndip Agbor, V. & Noubiap, J. J. Calcium supplementation and cardiovascular risk: A rising concern. J. Clin. Hypertens. (Greenwich). 19, 640–646 (2017).

103.      Fenton, J. I., Hord, N. G., Ghosh, S. & Gurzell, E. a. Immunomodulation by dietary long chain omega-3 fatty acids and the potential for adverse health outcomes. Prostaglandins. Leukot. Essent. Fatty Acids 89, 379–90 (2013).

104.      Hanson, S., Thorpe, G., Winstanley, L., Abdelhamid, A. S. & Hooper, L. Omega-3, omega-6 and total dietary polyunsaturated fat on cancer incidence: systematic review and meta-analysis of randomised trials. Br. J. Cancer 122, 1260–1270 (2020).

105.      Koeth, R. A. et al. Intestinal microbiota metabolism of L-carnitine, a nutrient in red meat, promotes atherosclerosis. Nat. Med. 19, 576–85 (2013).

106.      Wang, Y. et al. Formaldehyde produced from d-ribose under neutral and alkaline conditions. Toxicol. reports 6, 298–304 (2019).

107.      Chen, Y. et al. d-Ribose contributes to the glycation of serum protein. Biochim. Biophys. acta. Mol. basis Dis. 1865, 2285–2292 (2019).

108.      Yu, L. et al. D-ribose is elevated in T1DM patients and can be involved in the onset of encephalopathy. Aging (Albany. NY). 11, 4943–4969 (2019).

109.      Sinatra, S. T. & Caiazzo, C. (D)-Ribose supplementation in the equine: lack of effect on glycated plasma proteins suggesting safety in humans. J. Am. Coll. Nutr. 34, 108–12 (2015).