B vitamins are essential for brain function and are generally safe to consume in higher amounts than recommended. However, many people and definitely PWP, have deficiencies in one or more B vitamins, which can negatively affect brain function. Previous research has focused on three B vitamins (folate, vitamin B12, and vitamin B6) and their relationship to brain function, but the effects of other B vitamins have been largely ignored. The evidence on the effectiveness of supplementing with these three vitamins alone is inconclusive. Some argue that future research should focus on specific subgroups and use more sensitive measures. However, a more rational approach would be to study the effects of supplementing with the full range of B vitamins at higher doses. Research on multivitamins containing a full range of B vitamins suggests significant benefits for brain function. Research with all B vitamins is unlikely to have downsides and may provide a more comprehensive understanding of their effects. It is also important to consider the interactions between B vitamins and other nutrients. Overall, future research should explore the acute and chronic effects of a full range of B vitamins on brain function, rather than solely focusing on a small subgroup of vitamins.
I hadn't read this 2016 review by David O Kennedy before, but I don't want to keep it from you. It contains particularly interesting insights and supports my key points regarding the importance of a balanced diet but also the balanced intake of supplements, especially B vitamins.
B6 - The upper limit of 100 mg per day, as set forth in this review, is a good, appropriate, practical number: "The final B vitamin with an ascribed upper limit is vitamin B6 which has an upper limit set at 100 mg/day (approximately 75 × RDA) in the US on the basis of case reports of reversible sensory neuropathy following doses in excess of 1000 mg taken for extended periods. However, it is notable that multiple clinical trials entailing consuming up to 750 mg/day of vitamin B6 for a number of years have demonstrated a lack of neuropathic side effects"
Regarding vitamin B6, as I explained here: healthunlocked.com/cure-par... toxicity results from excess levels of the inactive form, pyridoxine, due to B2 deficiency.
Folate supplementation has been shown to be carcinogenic. I wrote about this here, tinyurl.com/ycdrz5lj with citations to medical literature. This review agrees that excess folate is adverse: "increasing the level of folate can mask the accrual of permanent neurological damage associated with a specific vitamin B12 deficiency ... A striking illustration of this was provided by an epidemiological study by Morris et al. ...who reported that high folate status was associated with protected cognitive function, but only in those with normal vitamin B12 status, with this relationship reversed in participants with low vitamin B12 status. For this group, high folate status exacerbated the detrimental effect of vitamin B12 deficiency ... It should also be noted that evidence suggests a potential detrimental effect of consuming high doses of folic acid, and therefore raised levels of un-metabolised folic acid, on normal folate metabolism and immune function. High folate levels may ... exert biphasic effects with regards to cancer; conferring protection at lower concentrations but increasing carcinogenesis at higher concentrations."
B12: "meta-analysis ... of the results of vitamin B12 supplementation studies with doses ranging from approximately 1 RDA up to 400 RDA (i.e., 1000 µg) administered for between four weeks and two years, showed that for every doubling of intake above the RDA, blood levels of Vitamin B12 continued to increase by 11%, while methylmalonic acid levels, an indicator of deficiency, decreased by 7%. This dose response is potentially most relevant to older adults (>50 years), who typically suffer age associated malabsorption of dietary vitamin B12 and therefore high levels of insufficiency. Certainly, in a dose-response study, Eussen ... found that the most effective dose for normalising vitamin B12 status in marginally deficient older adults was 500 µg/day (200 × RDA)."
As we can see by the foregoing passages, this review definitely does NOT support the idea that some kind of "balanced" intake of B vitamins is appropriate. Instead, the effect of each B vitamin must be considered individually and dosage tailored according to circumstances. Also, as evidenced by the foregoing, my posts about vitamins and this review are in agreement.
You naturally only read what you want to read. 😉 As far as I'm concerned, it's not about the (safe) dosages of the vitamins. It should by now be clear that we don't see eye to eye on that. This 2016 study is also quite outdated in that regard, as the safety margins for B6 in the EU have been significantly revised since then. But that's not what I want to discuss further at the moment; we can do that another time. 🐂
No, what concerns me here is the recognized importance of not only focusing on the well-known 3 (B6/B9/B12) when it comes to reducing high homocysteine levels, but also shifting the focus to include all B vitamins, including B1, B2, B3, and B5. Interestingly, vitamin B8, also known as biotin, is not mentioned in this context, but I believe it also plays a role in homocysteine metabolism.
It is evident that further research is needed on the interaction of B vitamins, or better yet, all vitamins. The desired dosage for this purpose is still up for debate. While the absorption factor of some individual B vitamins is approximately known to determine this more accurately, the influence of the interaction between B vitamins is still too unclear to establish an adequate intake.
I read the reference that you provided and cited the items that are in contention.
I have no objection to additional focus on the other vitamins that you mentioned. I have pointed out the importance of vitamin B2 on many occasions. Vitamin B1 is already the subject of much attention in the Parkinson's community.
PwP are noted for often times having lower B12 and B6 levels than their healthy counterparts or controls in studies. Low B12 and B6 can contribute to high homocysteine levels which are considered inflammatory. Homocysteine is typically at elevated levels in PwP. Elevated homocysteine levels may be associated with disease progression in PD. It is also associated with peripheral neuropathy. Homocysteine is also thought to contribute to cardiovascular disease (CVD) which people with PD are at increased risk for. CVD is the number one cause of death in the world accounting for roughly 30% of deaths in the world each year.
Testing and bringing your B12 and B6 levels well into the optimal range can lower homocysteine, which is something that PwP should do as part of their health maintenance plan, but you should remind your doctor of testing these important B vitamins at your regular visits to make sure your B12 and B6 levels remain optimal because low B12 and B6 is associated with cognitive impairment and a more rapid rate of disease progression.
B12 and B6 are two of the disease variables that you can easily maintain with your doctor's assistance.
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