There are many different types of vitamins, all of which have important functions within our body. Vitamin B6, also commonly known as pyridoxine, has a number of key properties, including allowing the body to use and store energy from proteins and food and helping to form haemoglobin. It also plays a role in metabolising proteins, carbohydrates and lipids (1). It is found in a wide variety of foods such as pork, fish, bread, soya beans, peanuts, milk, potatoes, vegetables, and eggs. B6 is the generic name for six compounds with vitamin activity: pyridoxal, pyridoxine, pyridoxamine and their 5-phosphate esters (2).
Recommended daily allowance of B6?
Most individuals should be able to achieve their daily recommended allowance of B6 – 1.4mg for men and 1.2mg for women – through eating a varied and balanced diet. Foods containing B6 should be eaten daily as no reserves can be stored in the body. Vitamin B6 is commonly available as a nutritional supplement in the form of multivitamin tablets that can be bought over the counter. Whilst taking doses between 10-200mg per day over a short period of time is not considered to be harmful, there are some concerns regarding their long term use and a condition known as peripheral neuropathy, in which there is a loss of feeling in the arms and legs. A recent systematic review of the available literature suggests that prolonged use of Vitamin B6 at a dose > 50mg per day may be harmful and should be discouraged (3). Generally, healthcare professionals will always advise patients to attempt to meet their RDA for Vitamin B6 through dietary means rather than by supplementation.
Who may need Vitamin B6 supplementation?
True deficiencies of B6 are very rare in most countries, although some groups, often as a result of illness, will have marginal levels of B6 that require supplementation. These groups will also often have deficiencies in other Vitamin B groups such as Vitamin B12 and folic acid (4). People who have anaemia, poor renal function or autoimmune disorders such as rheumatoid arthritis are at risk of B6 deficiency, as are patients who have celiac disease, ulcerative colitis, Crohn’s disease and other malabsorptive autoimmune disorders. There has been some discussion that B6 supplements can help reduce the risk of CVD and stroke, although there is no evidence to support this. Similar assertions that Vitamin B6 can play a role in reducing cancer incidence are unfounded, with a recent study carried out by a group of Norwegian researchers concluding that there is no association between B6 supplementation and cancer incidence, mortality or all-cause mortality (5).
Evidence for B6 supplementation
The essential role of Vitamin B6 in helping the body to function is unequivocal, yet little evidence exists regarding the role of Vitamin B6 supplementation for patients. This is most likely due to the fact that dietary means are the most routinely recommended approach for improving B6 levels, and it is very difficult to evaluate B6 supplementation in isolation as it is often given as a part of a Vitamin B combination. There is no good evidence to suggest B6 supplements significantly improve a number of cognitive functions, as had previously been hypothesised in a study of brain function in the elderly that had identified higher serum Vitamin B6 concentrations and memory test scores in a significant percentage of the studied population aged between 54-81 years (6). Following the publication of this test, The Cochrane Collaboration performed a systematic review of 14 RCTs investigating the relationship between Vitamin B6 and Vitamin B6 / folic acid combinations and their impact on cognitive function in people with normal cognitive function, ischemic vascular disease, or dementia. The study found there to be no positive impact on any of the patients studied, although the review also noted that the large majority of studies were poorly designed and of limited applicability to broader populations (7). Similar poor study designs have been documented in other systematic reviews that have ruled out a relationship between Vitamin B6 supplements and the reduction of premenstrual syndrome symptoms (8), nausea and vomiting in pregnancy (9), and the suppression of inflammatory cytokines in rheumatoid arthritis (10).
Is there any evidence to suggest that the activated form of vitamin B6 (pyridoxal-5-phosphate) is utilised better by the human body when compared to other forms of B6?
Pyridoxal-5-Phosphate (P5P) is the active form of B6, and all pyridoxine hydrochloride, pyridoxal and pyridoxamine must be converted inside the body by the liver to P5P in order for it to be effective. Individuals with particular autoimmune disorders have been evidenced to have difficulty converting B6 into its active P5P form, and as such it has been hypothesised that the ingestion of active PSP is utilised better by the body than standard B6 supplementation. However, there is very little formal literature available to back up this hypothesis, despite many recommendations from a range of nutritional outlets and organisations espousing the virtues of activated vitamin B6 when compared to other forms of B6.
A systematic review of all Vitamin B6 supplements in a study investigating the relationship between B6, B12, and folic acid supplementation and cognitive function found there to be no discernible difference in the various B6 preparations used. In many of the reported cases, placebo was recorded as being more effective than all B6 preparations (11). A similar study investigating the administration of standard B6 and P5P found there to be no difference in recorded effect in either mother or unborn child as part of a study investigating the role of B6 in neonatal health (12).
In conclusion, there is no available support for the hypothesis that P5P is more effective than inactive Vitamin B6. As currently suggested by many practitioners, changes in dietary habit are the most effective way to ensure that individuals receive their recommended daily allowance of Vitamin B6.
References
- Mackey A, Davis S, Gregory J. Vitamin B6. In: Shils M, Shike M, Ross A, Caballero B, Cousins R, eds. Modern Nutrition in Health and Disease (2005) 10th ed. Baltimore, MD: Lippincott Williams & Wilkins
- Subar AF, Krebs-Smith SM, Cook A, Kahle LL (1998) Dietary sources of nutrients among US adults, 1989 to 1991 J Am Diet Assoc 98:537-47
- Ghavanini AA, Kimpinski K (2014) Revisiting the evidence for neuropathy caused by pyridoxine deficiency and excess J Clin Neuromuscul Dis 16(1):25-31
- Bailey RL, Gahche JJ, Lentino CV, Dwyer JT, Engel JS, Thomas PR, et al (2011) Dietary supplement use in the United States, 2003-2006 J Nutr 141:261-6
- Ebbing M, Bonaa KH, Nygard O, Arnesen E, Ueland PM, Nordrehaug JE, et al (2009) Cancer incidence and mortality after treatment with folic acid and vitamin B12 JAMA 302:2119-26
- Riggs KM, Spiro A, 3rd, Tucker K, Rush D. Relations of vitamin B-12, vitamin B-6, folate, and homocysteine to cognitive performance in the Normative Aging Study (1996) Am J Clin Nutr 63:306-14
- Malouf R, Grimley Evans J (2003)The effect of vitamin B6 on cognition Cochrane Database Syst Rev CD004393
- Wyatt KM, Dimmock PW, Jones PW, Shaughn O'Brien PM (1999) Efficacy of vitamin B-6 in the treatment of premenstrual syndrome: systematic review BMJ 318:1375-81
- Niebyl JR (2010)Nausea and vomiting in pregnancy N Engl J Med 363:1544-50
- Chiang EP, Selhub J, Bagley PJ, Dallal G, Roubenoff R (2005) Pyridoxine supplementation corrects vitamin B6 deficiency but does not improve inflammation in patients with rheumatoid arthritis. Arthritis Res Ther 7:R1404-11
- Balk EM, Raman G, Tatsioni A et al (2007) Vitamin B6, B12 and folic acid supplementation and cognitive function: a systematic review of randomised trials Arch Intern Med 8;167(1):21-30
- Kang-Yoon SA, Kirksey A, Giacoia GP, West KD. Vitamin B6 adequacy in neonatal nutrition: associations with preterm delivery, type of feeding and vitamin B6 supplementation (1995) Am J Clin Nutr 62:932-942
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