Vitamin B₆ and coronary artery disease, myocardial infarction and ischaemic stroke

Vitamin B₆ and coronary artery disease

Table 1 summarises the human studies which addressed the relationship between vitamin B₆ status and CAD. Low plasma vitamin B₆ concentrations are not only associated with an increased risk for atherosclerotic diseases⁽Reference Robinson, Arheart and Refsum³⁰⁾ and more specifically with higher CAD incidence⁽Reference Robinson, Mayer and Miller^27, Reference Folsom, Nieto and McGovern^31, Reference Dalery, Lussier-Cacan and Selhub³²⁾ but the higher risk also appears to be independent of other recognised risk factors for CAD, including homocysteine⁽Reference Robinson, Mayer and Miller²⁷⁾. Moreover, adequate vitamin B₆ levels emerged as a protective factor for CAD⁽Reference Folsom, Nieto and McGovern³¹⁾. In a prospective design study, Folsom et al. ⁽Reference Folsom, Chambless and Ballantyne³³⁾ demonstrated that the risk of developing CHD within 5 years significantly decreased in parallel with increasing concentrations of plasma PLP⁽Reference Folsom, Chambless and Ballantyne³³⁾. The association between low PLP and CAD was, however, not confirmed in all studies⁽Reference Verhoef, Kok and Kruyssen^34, Reference Siri, Verhoef and Kok³⁵⁾ (Table 1).

Table 1

Vitamin B₆ and risk of CAD

CAD, coronary artery disease; PLP, pyridoxal 5′-phosphate; hs-CRP, high-sensitivity C-reactive protein; HR, hazard ratio; MI, myocardial infarction; RR, relative risk; tHcy, total homocysteine.

In addition to several epidemiological studies demonstrating a role for low PLP as an independent risk factor for CAD, some studies have shown that low PLP may be linked to CAD through inflammation. In an observational study conducted in an Italian population, a cohort of patients with angiography-defined, severe, multivessel CAD were compared with CAD-free subjects to evaluate the relationship between CAD risk and both plasma PLP concentrations and major markers of the acute-phase reaction⁽Reference Friso, Girelli and Martinelli¹¹⁾. An inverse relationship between plasma PLP and both high-sensitivity CRP (hs-CRP) and fibrinogen has been found, confirming previous findings of an inverse association between inflammatory markers and vitamin B₆⁽Reference Friso, Jacques and Wilson¹³⁾. The prevalence of low PLP (defined as PLP concentrations below 36·3 nmol/l, which was the median value in the control group) was significantly higher among CAD patients compared with controls⁽Reference Friso, Girelli and Martinelli¹¹⁾. The association between low plasma PLP concentrations and increased CAD risk was also independent of the major classical risk factors for atherosclerosis, including total plasma homocysteine. This association continued to be significant even when hs-CRP and fibrinogen were included in the multiple logistic regression models. The strength of this independent relationship was confirmed even after adjustments for a number of other conditions known to be associated with low concentrations of plasma PLP, including ageing, smoking status and impaired renal function. Results from the present study also showed that the combined presence of low PLP along with other major risk factors for CAD, such as higher hs-CRP and elevated LDL:HDL ratio, further increased the risk for CAD in a graded manner⁽Reference Friso, Girelli and Martinelli¹¹⁾.

These plasma PLP levels could be described as a mild PLP impairment compared with previous studies that had defined PLP impairment by concentrations as low as 20 nmol/l⁽Reference Robinson, Mayer and Miller²⁷⁾, suggesting that even a moderate impairment of this vitamin is sufficient to confer a higher risk for CAD. In a case–control study performed by Lin et al. ⁽Reference Lin, Cheng and Liaw³⁶⁾, low PLP concentrations (defined as PLP below 30 nmol/l) were associated with a significantly increased risk of CAD for angiography-documented patients compared with healthy controls, even after adjustments for hs-CRP⁽Reference Lin, Cheng and Liaw³⁶⁾. In a case–control study evaluating whether plasma PLP exerts an independent or a synergic effect with inflammation in elevating the risk of CAD, Cheng et al. ⁽Reference Cheng, Lin and Liaw³⁷⁾ confirmed that low PLP levels (below 20 nmol/l) are independently associated with higher CAD risk. The inverse relationship between PLP and hs-CRP was observed only within the control group.

Vitamin B₆ and myocardial infarction

A specific association between low plasma PLP and incidence of MI, the main thrombotic complication of CAD, is supported by early reports⁽Reference Kok, Schrijver and Hofman^38–Reference Vermaak, Barnard and Potgieter⁴¹⁾ and by subsequent case–control and prospective studies⁽Reference Chasan-Taber, Selhub and Rosenberg^42–Reference Gallant, Staszewski and Pozniak⁴⁵⁾, as listed in Table 2. Moreover, an association between lower dietary vitamin B₆ intake and higher risk of MI has also been suggested⁽Reference Chasan-Taber, Selhub and Rosenberg⁴²⁾.

Table 2

Vitamin B₆ and risk of myocardial infarction (MI)

PLP, pyridoxal 5′-phosphate; RR, relative risk; HR, hazard ratio.

A number of studies have observed an inverse association between plasma concentrations of vitamin B₆ and risk of MI, independent of known CAD risk factors⁽Reference Page, Ma and Chiuve^44, Reference Verhoef, Stampfer and Buring⁴⁶⁾, though not all studies confirmed this independent association⁽Reference Dierkes, Weikert and Klipstein-Grobusch⁴⁷⁾. In a study evaluating heart transplant recipients, it has been observed that about 21 % of the patients showed lower PLP concentrations and that only 9 % of those with lower plasma PLP levels did not have CVD complications⁽Reference Nahlawi, Seshadri and Boparai⁴⁸⁾. Subjects in the highest quintile of PLP had a significantly reduced risk of MI but adjustment for either low-grade inflammation or smoking diminished this association⁽Reference Dierkes, Weikert and Klipstein-Grobusch⁴⁷⁾. With regard to the relationship between MI, vitamin B₆ and major markers of inflammation, results from early studies have shown that low plasma PLP levels are related to acute-phase reactants in the initial phase of MI development⁽Reference Vermaak, Barnard and Potgieter^41, Reference Vermaak, Barnard and Van Dalen⁴⁹⁾.

Vitamin B₆ supplementation, inflammation and CVD prevention

An early observation of patients given vitamin B₆ for inflammatory diseases or degenerative diseases found that subjects supplemented with vitamin B₆ had a lower risk of developing MI compared with patients who had not taken vitamin B₆⁽Reference Ellis and McCully⁵⁵⁾. Table 3 summarises the main studies in which B vitamin supplementation, including supplementation with vitamin B₆, has been performed. In the Nurses' Health Study, among women with no prior history of CAD, users of multivitamins containing folate and vitamin B₆ had a reduced risk of CAD⁽Reference Rimm, Willett and Hu⁵⁶⁾.

Table 3

Vitamin B supplementation, including vitamin B₆, and CVD

WAFACS, Women's Antioxidant and Folic Acid Cardiovascular study; MI, myocardial infarction; RR, relative risk; WENBIT, Western Norway B Vitamin Intervention Trial; AMI, acute myocardial infarction; HR, hazard ratio; NORVIT, Norwegian Vitamin Trial; CAD, coronary artery disease; HOPE-2, Heart Outcomes Prevention Evaluation 2; VISP, Vitamin Intervention for Stroke Prevention randomised control trial; tHcy, total homocysteine; cIMT, carotid intima-media thickness; US, ultrasound; RTR, renal transplant recipients.

Very few human studies have been performed to evaluate the modifications of major markers of inflammation during supplementation with B vitamins, including vitamin B₆, despite the association with either folate and/or vitamin B₁₂⁽Reference Peeters, van Aken and Blom^57, Reference Palmas⁵⁸⁾. Furthermore, results from these studies have shown that CRP and pro-inflammatory IL levels are unchanged after vitamin supplementation⁽Reference Peeters, van Aken and Blom^57, Reference Palmas⁵⁸⁾. Antioxidant activity of vitamin B₆ supplementation has been observed in a study performed on rats, but the exact mechanism is unclear⁽Reference Mahfouz and Kummerow⁵⁹⁾.

Several large, prospective trials have been conducted in recent years with the principal aim of studying the effects of lowering serum homocysteine concentrations with the use of B vitamins, including vitamin B₆, on cardiovascular events⁽Reference Toole, Sane and Bettermann^60, Reference Bønaa, Njolstad and Ueland⁶¹⁾.

Overall, the most compelling data from vitamin supplementation studies have demonstrated that vitamin B₆ is not effective for preventing the recurrence of cardiovascular events, including CAD, peripheral vascular disease and stroke⁽Reference Wilmink, Welch and Quick^54, Reference Albert, Cook and Gaziano^62, Reference Toole, Malinow and Chambless⁶³⁾.

Only a few small trials, performed with renal transplant patients that have hyperhomocysteinaemia and subjects at risk for cerebral ischaemia, have demonstrated the effectiveness of vitamin B₆ supplementation with folate and vitamin B₁₂ on carotid artery intima-media thickness progression⁽Reference Marcucci, Zanazzi and Bertoni^64, Reference Till, Rohl and Jentsch⁶⁵⁾. This marker for subclinical atherosclerosis was also evaluated in another recent double-blind, placebo-controlled, randomised clinical trial⁽Reference Hodis, Mack and Dustin⁶⁶⁾. Vitamin supplementation significantly reduced subclinical atherosclerosis progression only in subjects at low risk for CVD, with total plasma homocysteine concentrations equal to or above 9·1 μmol/l⁽Reference Hodis, Mack and Dustin⁶⁶⁾. Other trials evaluated CAD patients for the effects of B vitamin supplementation, though the interpretation of the results was ambiguous. Supplementation with vitamin B₆, folate and vitamin B₁₂ after coronary angioplasty decreased the rate of restenosis and the need for revascularisation⁽Reference Schnyder, Roffi and Pin⁶⁷⁾, while supplementation after coronary stenting increased the risk of in-stent restenosis and the need for target-vessel revascularisation⁽Reference Lange, Suryapranata and De Luca⁶⁸⁾.

Despite the advantage of large randomised intervention studies, wisdom from the studies of cancer chemoprevention with folate clearly suggests that two critical factors should be taken into account in the aforementioned trials: time and dose of B vitamin supplementation. Nutritional intervention is indeed considered to be a two-edged sword, where a beneficial effect may be observed with nutritional support in the prevention phase and a disease-aggravating effect may be observed after the onset of illness, with nutritional support actually fuelling the disease process. This observation may certainly apply to folate supplementation, which can effectively prevent the onset or progression of disease in the early phase, while it may accelerate the progression of disease in the late phase. It can therefore be speculated that continuous supplementation with a single non-physiological form of vitamin supplements might contribute to unexpected or even harmful outcomes, even in the at-risk condition of having an impaired vitamin B₆ status. Furthermore, the major endpoints of these studies were those of evaluating the effect of lowering plasma homocysteinaemia on the recurrence of established disease, mainly by the simultaneous use of various B vitamins that have many additional functions other than that of lowering total plasma homocysteine. Little information, however, is available regarding both the effects of vitamin B₆ supplementation on inflammatory markers and the correct dose and timing to be followed to avoid the possible harmful effect of excessive or inappropriate vitamin B₆ supplementation. This information that would be needed for a possible primary or secondary preventive approach using vitamin B₆ is to be developed. Further specific studies are required to deepen our knowledge in this regard.

Even if there is consistently a lack of benefit in secondary prevention of CVD with B vitamin supplementation, with or without vitamin B₆ (Western Norway B Vitamin Intervention Trial⁽Reference Ebbing, Bleie and Ueland⁶⁹⁾, Women's Antioxidant and Folic Acid Cardiovascular study⁽Reference Albert, Cook and Gaziano⁶²⁾, Vitamin Intervention for Stroke Prevention randomised controlled trial⁽Reference Toole, Malinow and Chambless⁶³⁾, Norwegian Vitamin Trial⁽Reference Bønaa, Njolstad and Ueland⁶¹⁾, Heart Outcomes Prevention Evaluation 2⁽Reference Lonn, Yusuf and Arnold⁷⁰⁾), it should also be considered that all the aforementioned studies are quite diverse from one another in terms of the time period of supplementation. In fact, one may raise the point that the time period of supplementation is especially critical to reach positive outcomes or avoid possible harmful effects in terms of the rate of CVD events⁽Reference Loscalzo⁷¹⁾. However, despite the apparently clear outcomes⁽Reference Loscalzo⁷¹⁾, it could be argued that a potential benefit that modifies secondary prevention outcomes may not be observed over a period of moderate duration (between 2 and 5 years for the Norwegian Vitamin Trial, Heart Outcomes Prevention Evaluation 2 and Vitamin Intervention for Stroke Prevention studies or of about 7 years for the Women's Antioxidant and Folic Acid Cardiovascular study).

Furthermore, the negative results of vitamin supplementation trials, including vitamin B₆ use, do not preclude the possibility of a protective effect in primary prevention. It could be difficult, however, to demonstrate that vitamin B supplementation is ineffective in patients who have had a clinical vascular event, while effective in those without a clinical event or with subclinical atherosclerosis. Clinical trials for primary prevention may require a longer duration and larger populations in order to answer the key question on whether vitamin B₆ supplementation is effective in preventing CAD before the first vascular event or in younger life.

Studies are needed to find the specific time and optimal dose of vitamin B₆ in order to maximise efficacy, minimise adverse effects and identify targets for vitamin B₆ interventions on the basis of genetic susceptibility and environmental factors. A better understanding of the mechanisms underlying the relationship between CVD and vitamin B₆ may indeed be extremely helpful in designing the most accurate preventive strategies.

Inflammation and vitamin B₆-related atherogenesis

PLP functions as a coenzyme in more than 100 reactions that are involved in the metabolic pathways of neurotransmitters as well as in the metabolism of amino acids, lipids and carbohydrates⁽Reference Endo, Nishiyama and Otsuka⁷²⁾. PLP also takes part in other significant pathways related to immune function⁽Reference Meydani, Hayek and Coleman⁷³⁾, thrombosis^(74, Reference Schoene, Chanmugam and Reynolds⁷⁵⁾ and inflammation⁽Reference Roubenoff, Roubenoff and Selhub¹⁷⁾, all of which are crucial mechanisms in every stage of the atherosclerotic process.

Furthermore, PLP is implicated in the synthesis and repair of both nucleic acids and proteins. Low vitamin B₆ concentrations could thus reflect an increased consumption of PLP in the accelerated synthesis of cytokines⁽Reference Doke, Inagaki and Hayakawa⁷⁶⁾ and in the activation and proliferation of lymphocytes, both of which are key events in the inflammatory process⁽Reference Meydani, Ribaya-Mercado and Russell^77, Reference Kwak, Hansen and Leklem⁷⁸⁾.

Considering the epidemiological evidence of a role of vitamin B₆ in inflammatory-related diseases and the observed relationship with inflammatory markers⁽Reference Friso, Girelli and Martinelli^11, Reference Saibeni, Cattaneo and Vecchi^16, Reference Chiang, Smith and Selhub^18, Reference Morris, Sakakeeny and Jacques⁷⁹⁾, it is plausible that vitamin B₆ plays a role in CVD pathogenesis through mechanisms linked to inflammation (Table 4).

Table 4

Vitamin B₆ and inflammation

NHANES, National Health and Nutrition Examination Survey; CRP, C-reactive protein; PLP, pyridoxal 5′-phosphate; hs-CRP, high-sensitivity CRP; CAD, coronary artery disease; PL, pyridoxal; RA, rheumatoid arthritis; ESR, erythrocyte sedimentation rate; ARIC, Atherosclerosis Risk in Communities; IBD, inflammatory bowel disease; tHcy, total homocysteine.

Therefore, with the knowledge that systemic acute-phase markers are solid and independent risk factors for CAD⁽Reference Ridker^80, Reference Ridker, Hennekens and Buring⁸¹⁾, that inflammation exerts an essential role in all stages of the atherosclerotic process⁽Reference Grundy⁸²⁾ and the possibility that vitamin B₆ has a role in inflammatory processes, several mechanisms were proposed linking low vitamin B₆ and CVD using cell culture studies, animal studies⁽Reference Endo, Nishiyama and Otsuka⁷²⁾ and clinical trials.

Animal studies have reported that inflammation reduces circulating and hepatic concentrations of vitamin B₆. Plasma PLP is considered as a sensitive indicator of tissue vitamin B₆ status⁽Reference Parker, Marshall and Roberts^3–Reference Leklem^7, Reference Chiang, Bagley and Roubenoff^15, Reference Chiang, Smith and Selhub¹⁸⁾. As shown in Fig. 1, it is thus possible that, in patients in an inflammatory state, PLP is mobilised from the liver and peripheral tissues to the sites of inflammation⁽Reference Chiang, Bagley and Selhub¹⁹⁾. Plasma PLP levels are known to be inversely related to TNF-α production and other inflammatory cytokines in RA⁽Reference Roubenoff, Roubenoff and Selhub¹⁷⁾. It has also been reported that low plasma PLP concentrations are inversely related to both plasma fibrinogen⁽Reference James, Vorster and Venter⁸³⁾ and CRP⁽Reference Friso, Girelli and Martinelli^11, Reference Friso, Jacques and Wilson¹³⁾, with a robust and independent association of other major biomarkers related to vitamin B₆ metabolism⁽Reference Friso, Girelli and Martinelli¹¹⁾. Moreover, inflammatory status increases oxidant stress, which results from an imbalance between oxidant production and antioxidant defences (Fig. 1). All these conditions characterised by the increase in inflammatory cytokines, fibrinogen, CRP and superoxide radicals may induce the consumption of vitamin B₆, with a consequent reduction of PLP plasma levels and its antioxidant effect, and, at the same time, they may favour a thrombogenic effect, thus triggering an impairment of endothelial function which is a key event in the pathogenesis of atherosclerotic processes (Fig. 1)⁽Reference Heitzer, Schlinzig and Krohn⁸⁴⁾. PLP has also been described to have an inhibitory effect on endothelial cell proliferation⁽Reference Matsubara, Matsumoto and Mizushina^85, Reference Matsubara, Mori and Akagi⁸⁶⁾. The persistence of a chronic inflammatory condition may result in the depletion of vitamin B₆, which might then contribute to a sustained chronic inflammatory response (Fig. 1).

Fig. 1

A simplified scheme of the proposed possible mechanisms for the relationship between low vitamin B₆ and CVD. This figure is a simplified representation of some of the possible mechanisms through which an impaired vitamin B₆ status has been hypothesised to exert its effect in atherosclerotic disease process. As shown, it is possible that vitamin B₆ is mobilised from the liver and peripheral tissues to the sites of inflammation which is characterised by an increase in C-reactive protein (CRP), fibrinogen, superoxide radicals (SOR), TNF-α as well as other inflammatory cytokines. Plasma vitamin B₆ (pyridoxal-5′-phosphate) concentrations are reported to be inversely related to TNF-α and other inflammatory cytokine production as well as major markers of inflammation such as CRP and fibrinogen, in chronic inflammatory processes. The inflammatory status, furthermore, increases oxidant stress, which results from an imbalance between oxidant production (SOR) and antioxidant defences and may induce the consumption of vitamin B₆ with a consequent reduction of the active form of vitamin B₆ (pyridoxal-5′-phosphate) plasma levels and its antioxidant effect and, at the same time, it may facilitate a thrombogenic effect which then triggers the impairment of endothelial function, a key event in the pathogenesis of atherosclerosis. Vitamin B₆ has also been described to have an inhibitory effect on endothelial cell proliferation; therefore, the reduction of vitamin B₆ (pyridoxal-5′-phosphate) plasma levels induced by inflammatory process may further favour the mechanisms leading to atherogenesis. , Cellular cycle; , vitamin B₆; M, mitosis cell phase; S, synthesis cell phase; G1, gap 1 cell phase; G2, gap 2 cell phase.

Most of the evidence demonstrates a potential role for vitamin B₆ in inflammatory processes where the low vitamin B₆ status in inflammation-related illnesses appears to result not from lower intake or excessive catabolism of PLP but from the inflammatory process underlying the disease itself⁽Reference Morris, Sakakeeny and Jacques⁷⁹⁾.

Although vitamin B₆ represents an important coenzyme in the metabolism of homocysteine, a recognised risk factor for thrombosis, the role of PLP in atherosclerosis is only partly related to its function in the one-carbon pathway. Several studies have thus supported a role for vitamin B₆ in the risk of CVD⁽Reference Robinson, Mayer and Miller^27, Reference Folsom, Nieto and McGovern^31, Reference Chasan-Taber, Selhub and Rosenberg^42, Reference Verhoef, Stampfer and Buring⁴⁶⁾ and stroke⁽Reference Kelly, Shih and Kistler²⁹⁾, independent of homocysteine and other risk factors. A hypothesis is that vitamin B₆ could be directly implicated as a cofactor in an anti-inflammatory mechanism where the utilisation of the vitamin results in its consumption, and the consequent low vitamin B₆ concentrations could support and amplify the inflammatory process, thereby leading to chronic progression of inflammatory disease. Indeed, a mild deficiency of vitamin B₆ may be associated with an increased risk, not only of atherosclerosis, but also of other chronic inflammatory diseases such as RA⁽Reference Chiang, Smith and Selhub^18, Reference Woolf and Manore⁸⁷⁾ and inflammatory bowel diseases⁽Reference Saibeni, Cattaneo and Vecchi¹⁶⁾. A number of studies have highlighted the relationship between PLP and inflammation, showing an inverse association between vitamin B₆ and major markers of inflammation, including plasma fibrinogen concentration⁽Reference James, Vorster and Venter⁸³⁾, erythrocyte sedimentation rate and CRP⁽Reference Friso, Jacques and Wilson¹³⁾. In the population-based Framingham Heart Study cohort, the association between PLP and CRP was strong and independent of other major biomarkers related to vitamin B₆ metabolism⁽Reference Friso, Jacques and Wilson¹³⁾, supporting a possible role for plasma PLP in inflammatory processes.

Some reports did not support this observation⁽Reference Folsom, Desvarieux and Nieto⁸⁸⁾, such as the study by Folsom et al. ⁽Reference Folsom, Desvarieux and Nieto⁸⁸⁾, conducted among healthy middle-aged adults in the Atherosclerosis Risk in Communities Study, which did not find an inverse association between CRP and PLP. However, the authors did observe that lower plasma PLP and dietary vitamin B₆ were associated with a higher leucocyte count, though this association was not found with the use of vitamin supplements⁽Reference Folsom, Desvarieux and Nieto⁸⁸⁾. It should also be taken into account that some diversity in the observations reported by the studies may be due to the different methods utilised to measure plasma PLP, although the methods used by most studies are considered highly reliable for the assessment of vitamin B₆ status⁽Reference Friso, Girelli and Martinelli^11, Reference Chiang, Bagley and Roubenoff^15, Reference Folsom, Desvarieux and Nieto^88–Reference Kimura, Kanehira and Yokoi⁹⁰⁾. The majority of studies, however, confirmed the inverse correlation between PLP and major markers of inflammation in various inflammation-related diseases. In subjects affected by RA⁽Reference Chiang, Bagley and Selhub^19, Reference Chiang, Selhub and Bagley²⁴⁾, PLP was associated with erythrocyte sedimentation rate, CRP levels and other markers of disease activity and severity, suggesting that impaired vitamin B₆ status is a result of inflammation. It also appeared that the relationship between lower vitamin B₆ and increased inflammation in these RA patients could be tissue-specific⁽Reference Chiang, Selhub and Bagley²⁴⁾.

Plasma PLP concentrations are also altered in subjects who have acute diseases with an evident underlying inflammatory condition. Vasilaki et al. ⁽Reference Vasilaki, McMillan and Kinsella⁹¹⁾ observed that in patients admitted to an intensive therapy unit, high concentrations of CRP, PLP and intracellular pyridoxal levels were significantly lower in those critically ill patients than in the group of subjects taken as controls.

Further support for the hypothesis of a link between vitamin B₆ and inflammation can be found in an analysis of data from a large population-based survey from participants in the 2003–4 National Health and Nutrition Examination Survey. Results showed that higher vitamin B₆ intakes are protective against inflammation, as indicated by hs-CRP concentrations. Moreover, the level of vitamin B₆ intake that was associated with maximum protection against vitamin B₆ inadequacy was elevated in the presence of inflammation compared with its absence⁽Reference Morris, Sakakeeny and Jacques⁷⁹⁾.

A strong inverse association between vitamin B₆ status, as measured by plasma PLP concentration, and the inflammatory marker CRP was also observed recently in a cohort of elderly Puerto Ricans living in Massachusetts⁽Reference Shen, Lai and Mattei⁹²⁾. In the present study, chronic inflammatory conditions, such as the metabolic syndrome, diabetes and obesity, were significantly associated with lower plasma PLP. The patients affected by such diseases were also significantly more likely to demonstrate vitamin B₆ inadequacy. Furthermore, lower PLP plasma concentrations were associated with oxidative stress, as indicated by higher urinary concentrations of 8-hydroxydeoxyguanosine, a marker of DNA damage and oxidative stress⁽Reference Shen, Lai and Mattei⁹²⁾. Authors concluded that vitamin B₆ status may influence CAD risk through mechanisms that link vitamin B₆ to inflammatory processes rather than mechanisms related to the role of vitamin B₆ in homocysteine metabolism⁽Reference Shen, Lai and Mattei⁹²⁾.