What is the Best Dose for B Vitamin Supplements?
Taking a good quality B vitamin supplement can have tremendous benefit. For example, pregnant women who supplement with folic acid during pregnancy. We know that people are not going to stop supplementing with B vitamins, nor do they necessarily need to, so our job here is to present the data in a useful way so you can make an educated decision when it comes to choosing a brand and a healthy B vitamin dose. Yes, B vitamins are a good thing, an essential thing to human health. However, the common thinking in supplement circles that because B vitamins are water soluble, they can be taken in larger and larger doses with no consequences, isn’t the whole story. In fact, at certain populations and at certain doses, supplementing with B vitamins seems to increase the risk for certain types of cancers. There are four main studies we’re going to reference here and I’ve summarized the findings in a giant table to the end of the post, but I’ll go through each one independently to describe the headline findings, and importantly the doses of B vitamins and groups assessed.
- Studies linking B vitamin supplementation to cancer risk
- Evaluating B Vitamin Supplements
- B Complex supplements with more conservative doses
- Take home message
- B Vitamin and Cancer Risk Diagram
Studies linking B vitamin supplementation to cancer risk
B vitamin intake and cancer in women – 2008The first article we’ll look at is this one from 2008,1 which is the earliest paper we’ll look at, and which looks not only at folate supplementation, but also supplementation with thiamin, riboflavin and niacin. At the outset, the authors discuss the paradox of folate supplements. On the one hand, folate is necessary for the repair of DNA and methylation, but on the other hand, too much folate has been shown to fuel the growth of cancer cells.2 Simply put, the one carbon cycle, which contains many of those genes we mention above, relies on B vitamins to function correctly. We’ve covered what happens when there is a lack of activity, but in this instance the authors are interested in what happens if this cycle is supercharged by supplementing. The authors decided to investigate any effect using a large previously existing cohort generated as part of the “The Canadian National Breast Screening Study”. For this study the dietary intakes and cancer outcomes of 49,654 Canadian women between the ages of 40-59 were followed for five years between 1980 and 1985. Now this is a key point, as the study was retrospective and initially wasn’t interested in B vitamin or multivitamin intake, the authors have had to estimate vitamin intake based on the provided nutritional information and population averages, which is why the highest doses look a bit odd. Most importantly using this methodology the authors didn’t detect any significant association between their highest dose groups and cancer risk. None of the B vitamins were thought to be dangerous in this study. Score on for B vitamin supplements.
Cancer, Folic Acid and Vitamin B12 – 2009Moving on to 2009, and a JAMA study, we see a different take on the study format. Rather than being retrospective, the authors of this study prospectively set out to assess cancer risk in relation to vitamin B dosing. In that way, this is a better study than the 2008 study. Doses and timing are much more accurate and so it should be easier to identify any associations. In this study, 6,837 patients from two Norwegian patient groups, with existing heart disease, were treated with certain B vitamins or a placebo between 1998 and 2005. Interestingly, the study authors identify a significant increase in cancer risk when patients supplemented with folic acid(0.8 mg/d) and vitamin B12 (0.4 mg/d) for 39 months, leading to an increased risk of cancer incidence (cancer being detected during the study period – hazard ratio 1.2) and cancer mortality (dying from cancer within the study period HR 1.38), in both instances lung cancer was especially increased. Quite a striking effect considering the doses and how closely these could mimic a daily supplementation regime. But it is important to remember that these individuals had a pre-existing diagnosis of heart disease and so this may not be representative of an otherwise healthy population. Nonetheless, doses of 0.8mg of folic acid and 0.4mg of B12 are very common in dietary supplements, so this study offers a real warning sign to those who mega dose B vitamin supplements over a long period of time.
B vitamins, methionine and risk of lung cancerWhen you see lung cancer the immediate thought is smoking, so it’s no surprise that based on the above study two quite similar papers came out in 2012 and 2013. The obvious question is what do B vitamins do to those who are already at risk of cancer? Does supplementing with B vitamins “turn on” the cancer? Both of these studies approached the question in the same way, using a retrospective study to investigate an already existing data set. In the case of the first paper this was the “The Melbourne Collaborative Cohort Study” which followed 41,514 men and women between 40-69 between 1990-1994 (and beyond for many individuals), and in the latter case “The Shanghai Women’s Health Study” which followed 74,941 women aged between 40 and 70. As with the first study, both of these studies relied on using retrospective data points, and as the main focus of the study wasn’t B vitamins, individuals were group based on their general nutritional intake, and approximate B vitamin values calculated. Interestingly, in both studies the increase in cancer risk in individuals with a high vitamin B intake wasn’t observed. BUT, the high dose groups in these studies are most likely below the levels of B12 used in the 2009 JAMA study. For example in the JAMA study patients received 0.4mg/d of vitamin B12 whereas the dose was 0.04mg/d in the 2013 Chinese study. Also both of these studies reported a protective effect for vitamin B2 in smokers, or those who had previously smoked, reducing their risk of developing lung cancer.
Long-Term B Vitamin Use and Lung Cancer Risk – 2017Performing clinical trials is expensive and very time consuming so retrospective studies applied to existing data sets are a vital part of research. But as you’ve seen above, trying to calculate B vitamin intake after the event is not the most accurate way of addressing things. Enter this 2017 study which looked at 77,118 men and women between the ages of 50 and 76 with defined vitamin B intakes over 10 years, these defined intakes were taken as either multivitamins or individual dosings and a huge raft other metrics were also recorded. Their take home findings were pretty startling:
- In women high dose vitamin B6, B12 or folic acid was not associated with an increased cancer risk.
- In men both vitamin B6 (20 mg/d – HR 1.82) and vitamin B12 (0.55 mg/d – HR 1.98) were associated with an increased lung cancer risk.
- For current smokers this risk was even worse (B6 HR 2.93 and B12 HR 3.71).
- This was only observed for single supplements not multivitamins.
The chart shows Vit B12 1.5 mg having lower risk than 0.04 mg or 0.55mg ! Was that a typo?
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Could you add the reference for that 2017 study?
Also, based on the JAMA study, I’m not convinced b12 is a problem since there was no group that supplemented with just b12 so no way to know if b12 has anything to do with the effect or if it’s just the folic acid. The researchers themselves say the effect is probably mediated by the folic acid in the article discussion. Additionnally, they used cyanocobalamin which you say yourself is the “lower quality” form of b12. Thridly, the baseline level of b12 was 477 pg/mL and was raised to 761 pg/mL in the study group. My level is 210 pg/mL and my doctor says it’s fine, it’s “in the range”. But I feel better when I supplement with 2400 mcg (methylcobalamin + adenosylcobalamin) so I’m inclined to continue. Of course I want to take cancer risk seriously but based on my non-expert analysis of this study, I’m tempted to continue supplementing. Thoughts?
Appreciated your thoughts and review!