Study Links High-Dose B Vitamins With Kidney Decline in People With Kidney Disease

A number of studies have demonstrated a link between high blood concentrations of homocysteine, an amino acid that’s produced by the body, and the risk of developing conditions such as diabetic nephropathy (kidney disease), retinopathy (eye disease), and vascular conditions such as heart attack and stroke. Treatment with B vitamins has been shown to decrease the concentration of homocysteine in the blood, so researchers wondered whether therapy with B vitamins could, by extension, slow the progression of kidney disease and prevent complications affecting the blood vessels.


To test this out, scientists in Ontario, Canada, randomly assigned 238 people with Type 1 or Type 2 diabetes and diabetic nephropathy to be given either a single daily tablet containing 2.5 milligrams of folic acid, 25 milligrams of vitamin B6, and 1 milligram of vitamin B12, or a placebo (inactive) tablet. Participants had homocysteine levels and glomerular filtration rate (GFR; an indicator of kidney function) measured at follow-up visits every six months for up to three years.

The B vitamins appeared to be successful at lowering blood levels of homocysteine. However, this decrease did not translate into better health outcomes — in fact, the researchers found that people who had received B vitamins had a greater decrease in GFR, corresponding to poorer kidney function, than those who had received placebo and also had twice the rate of heart attack, stroke, and all-cause deaths at the end of the follow-up period.

The researchers speculate that the beneficial effect of lowering homocysteine levels might have been offset by toxicity associated with the B vitamins. According to author J. David Spence, MD, and colleagues, “Because B vitamins are water soluble, we suspect that while healthy people would excrete excess vitamins in urine, those with renal failure would not be able to do so, perhaps causing the adverse effects we have seen in this study. Vitamin B therapy may still be beneficial in people with normal kidney function, but this is clear evidence that high doses of vitamin B should not be given to those with kidney problems.”

To learn more, read the article “High Doses of B Vitamins Associated With Increased Decline in Kidney Function for Patients With Kidney Disease from Diabetes” or see the study’s abstract in the Journal of the American Medical Association.

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  • Donna Ann

    Hoe much is enough Vitamin Bs and how much rpotein shoud a person consume. My last kdney fuction test was Total protein 7.6 and the Range should be 6.3-8.2 (MG/DL) Albumin 4.4 and the Range should be 3.5-5.0 (MG/DL) SGOT (AST) 25 and the Range should be 14-59 (U/L)SGPT (ALT) 33 and the Range should be 9-72 (U/L) ALK P’TASE 91 and the Range should be 38-126 (U/L) TOTAL BILI 0.7 and the Range should be 0.2-1.3 (MG/DL) DIR.BILI 0.0 and the Range should be 0.0-0.3 (MG/DL)IND.BILI 0.8 and the Range should be 0.0-1.1 (MG/DL) maybe I am just starting to have a problem, but I think before I recognized that I hac a diabetes problem I perodicially had diabetes before I was diagonised with it. Like a prediabetic thing and I wonder if that can be true for nephropathy problems? How much is too much protein as this point in time? One page 207 of the The Best Of Diabetes Self-Management Book says that a low protein diet, byt doesn’t say how much protein. One book that I have claims that a chicken breast my have 25-30 grams on protein. Most people without diabetes are suppose to consume between 50-60 grams of protein a day.
    Please make comment
    Donna Ann

  • Dick

    Diane: This article leaves me a bit confused as to wheather I should or shouldn’t take my vitamin B. It seems you are saying that there is some increased benefit by taking B but then there isn’t. Can you put it into two sentences and be more precise?

  • Diane Fennell

    Hi Dick,

    Thanks for your question. The researchers had hypothesized that high-dose B vitamins might be able to slow the progression of certain complications, given the effect of these vitamins on homocysteine levels. However, they found the opposite: People taking the high-dose vitamins ended up having worse kidney function and more vascular complications than those who were taking a placebo (inactive treatment).

    Please note that the study participants were taking high doses of B vitamins: 2.5 milligrams of folic acid, 25 milligrams of vitamin B6, and 1 milligram of vitamin B12.

    You should discuss any vitamins or supplements you are taking with your health-care provider to determine what, if any, amount of each vitamin is right for you.

    Thank you for your interest in Diabetes Self-Management.

    Diane Fennell
    Web Editor

  • Laurie

    This article is quite confusing. Is a single dose of B12 okay? Also, for those of us that take Metformin, which has shown to cause a B12 deficiency, taking a B12 supplement is recommended.

  • Lazarus Long

    What is considered a mega-dose? I take a multi-vitamin once a day, specifically: Centrum Silver Ultra Men’s. The Centrum pill contains 6 mg of Vitamin B6 (300%), 300 mcg of Folic Acid (75%), and 100 mcg of Vitamin B12 (1,667%). The B12 seems like it might fall into the mega-dose category. Are there other good wide spectrum multi-vitamins that do not have such a high dose?

  • Amber

    To test this out, scientists in Ontario, Canada, randomly assigned 238 people with Type 1 or Type 2 diabetes and diabetic nephropathy.
    The patients tested already had diagnosed kidney problems from diabetes. In my viewpoint, we are dealing with an organ that in this studied population, has problems filtering- that includes vitamins and minerals. So potientially vit B may not be excreted as well in this particular population than in those with normal functioning kidneys. Most over the counter supplements are not absobed at 1oo% of what they are indicating is in there, B vitamins are water soluable. I would think they would get a totally different result in those with high homocysteine levels with no evidence of renal impairment (kidney problems).

  • linda

    The article could be much more specific. How much is too much? What are the recommendations? I take a multi vitamin and a single B complex 150%supplement.

  • Amber

    Donna Ann, the labs you listed do not really tell of your kidney function. GFR is the standard to determine if there are kidney problems, BUN and Creatinine can give a clue as well but are more sensitive to hydration status.
    Again, remember this is one study. They are not going to determine appropriate supplementation amounts for the general population based on one study. These individuals already had kidney problems, most people can get rid of excess B vitamins. If you have kidney problems you need to be limiting your supplements anyway and always inform the Dr and pharmacist. B vitamins are in animal protein, dairy, leafy dark greens, etc. You should not need to daily dose for supplements of this anyway and if you are, you are likely not absorbing it all anyway (low quality source). They have not set upper tolerable limits for B12- but it is probably one you don’t want to go too high in and not frequently take due to increased chances of issues. Those with B12 deficiencies may need to under a Dr. care. Excessive B12 causes symptoms such as numbness and tingling- but so does damage from elevate blood sugar!

  • robert

    I think they are saying like with water if you drink way too much you can actualy poison yourself

    too much of a good thing can be bad but that doesnt mean it isnt still a good thing in smaller amounts

  • Kathy Mack

    This article was interesting. I realize the patients in the study already had kidney disease but what about the same study using patients who don’t have kidney disease.
    I already have neuropathy in my feet. Some of it is from diabetes and the rest is from a foot injury that has affected the nerves in my foot.
    I had my B-12 levels checked because low B-12 levels can have the same symptoms as neuropathy. My B-12 levels were low and I am now on B-12 supplements 1000 mcg daily. Starting this I discovered there are several forms of vitamin B-12 such as Cyanocobalamin and MethylB or
    Methylcobalamin which is a fat soluble form of
    B-12. I started out with the former and changed to the latter form of B12 after much research and studying. MethylB12 is used in the treatment of neuropathy and I feel it is helping but it did not help immediately. At the same time if one’s B12 levels are normal then I don’t think B-12 supplementation is necessary. One should have their Vitamin B levels checked to make sure they are in normal range before supplementing with B Vitamins.

  • Ann

    My cardiologist has me on 1000mg of Niaspan, which as I’ve been told is a B vitamin. I also take one multivitamin a day. Does this constitute excessive B vitamin for me?

  • Shirley

    I am still confused with the B vitamin study. I don’t take a spectrum of B – I only take B-12 (500mgs) as a release from neuropathy symptoms – yet I still have “needles and pins pain in my feet and ankles. This study is frightening me – I don’t want to have kidney problems – my mother has end stage renal failure. My doctor knows I am taking B-12 supplements and has not suspended my use of same. I still don’t know if what I am taking is considered to be a mega-dose.

  • Jack Rhondeau

    Frankly I think this is a dangerous approach to concern people unnecessarily about Vitamin B usage. Case in Point; The posters above are all concerned whether they should discontue their vitamin regimen. I get upset when I see a small group test (not even a double-blind test) that doesn’t really pertain to the general population presented in a way to alarm people who might discontinue taking required medication. People, don’t pay attention to articles like this. Do what your doctor recommends… Period!!!

  • Henry Ford

    This ‘study’ is somewhat hard to believe. I find so much trash is being published under the guise of medical experimentation that you need to take it all in with some doubt. Remember, mega doses of the B vitamins have been used for years and years. (It has always been considered the cure-all for every disease.) It would seem to me that all these people would be on dialysis by now and that the results of overdosing this vitamin would be very obvious. Answer: take vitamin B and reduce your Homocysteine, BUT take it in moderate amounts! That sounds like good common sense until the next medical study contradicts the previous one!!! (lol)

  • Diane Fennell

    Thank you all for your comments. As several of our posters have mentioned, recommendations for vitamin intake in the general population cannot be set on the basis of one study alone. Only your doctor can determine what amount of vitamin supplementation is appropriate for you. Do not stop taking any of your medicines unless advised to do so by your health-care provider, and be sure to speak with him if you have any concerns about the medicines you are currently taking.

    Diane Fennell
    Web Editor

  • Gregg Milliken

    Ok but how much water were people given as a gudeline .I drink a gallon a day of distilled water and have used massive doses of B vtiamins! There are many other factors to be keyed into testing B vit. The last test I had actually showed that my kidneys were at top performance. Years ago I had some renal spillage .. So did the kidneys actually heal? I have had diabtes for 40 years and wrote a book on when I went blind! I now have 20/20 vision. I hope you investigate futher! My book is available at amazon .com Once I was Blind”.

  • granny Pat

    Gregg, Why drink distilled water? I was told distilled water will drain a persons body of all minerals.
    AS far as studies go….that’s all they are….studies. All people are different. So how can any study be true?

  • acampbell


    I also wanted to reiterate that this study used very high doses of B vitamins. For example, the amount of folic acid prescribed is six times the RDA for folic acid, and the amount of B6 was about 20 times the RDA for B6. You get nowhere near that amount in a standard multivitamin supplement. Also, I asked a renal doctor with whom I work and he said that, in usual doses, there is no evidence that taking B vitamins would be harmful. But as Diane and others have mentioned, it’s always good to practice moderation, and if you have any concerns, speak with your physician.

  • Alisha Ruiz

    I just wanted to say THANK YOU Jack Rhondeau!!! ENOUGH said:)

  • Daniel Muguko

    This is a very important revelation.

  • jim snell

    Oh no, another smoke screen to send the natives scurrying.

    For me, I was taking B12 when a1c was 13.3. Kidney s in grief and showing decreasing function.

    Drop a1c to 6.9 and keep down last year, kidneys stabalized and held solid numbers.

    More important fact is get the damm BG down. This report does not supply all its data nor indicate the extent of the diabetes in each member of survey and somebody else has to summarize for the non comprene vou.

  • jim snell

    Look folks, instead of sounding the Dive Horn; the real issue may be – taking high doses of B12 that result in higher than normal levels in blood etc may be issue. If one takes high doses to make up for reduced B12 due to metformin use, actual dose that results in more normal doses in blood should not be issue.

    Taking high doses as general statement needs some more explanation/data rather than shooting the shotgun in general direction of the turkeys causing them all to hop into the trees.

  • Brenda

    I’m interested in learning the effects of too much vitamin B for those without diabetes. With the new phase of energy drinks containing 2000% of the RDA of B6. I worry an overload of this product could hurt the kidneys and cause diabetes.
    Is this possible?

  • Carol brown

    Thank you for this article. AARP has recommended that seniors might benefit from the vitamin regime (B12,Folic acidand B6). I have stage 3 kidney disease. This would not be a good thing for me or people who are unaware theyhave kidney issues. It’s a silent disease.
    Iwas considering following their advice instead of taking statins. thanks again for the heads up.

  • Helen

    Dear Diane, great blog! Please can you get out the message that the reason the research subjects fared poorly on high -dose B12 was not due to the amount, but rather the TYPE of B12 used in the study.

    It seems that the researchers used ‘Cyanocobalamin’ – which as you guessed,is made from cyanide molecules. Cyanocabalamin is actually synthetic B12.

    In healthy persons, they can normally excrete the cyanide. In persons with stage 4 or end-stage kidney disease, they cannot do that easily. The study should have used the bioavailable, safe form of B12 — Methylcobalamin. This is the type that lowers homocystein levels and inflammation. Methylating vitamins turn on the things you want and turn off the things you don’t want.

    Here in Dr. Spence’s (the lead researcher’s) words is the suggestion to use methylcobalamin instead of cyanocobalamin B12 in the future- epecially in cases where the patient’s glomerular filtration rate is <50.$002fcclm.2013.51.issue-3$002fcclm-2012-0465$002fcclm-2012-0465.xml;jsessionid=622D3165A9804ED485C1FA2880A7A285

    Another problem was that high-dose folic acid was used rather than folate (non-synthetic form). Some synthetic vitamins are safe at high doses (i.e, ascorbic acid/vit C). Other synthetic vitamins are not, and can even act as growth factors for tumours (i.e, synethic dL vit E, synethic selenium, cyanocobalamin, synthetic folic acid and retinol/synthetic vitamin A).

    A lot of studies are confusing to read, to say the least, and newspapers tend to look at highlights of studies vs important details such as whether synthetic vitamins were used. Please everyone on this board, know that you can contact lead researchers and ask them questions. I have noticed that the most intelligent, most ‘secure’ academics are glad share important details with the public. They are normal everyday people and welcome your interest in their papers.

    • prioris

      excellent post helen. so many studies use the worst forms of b12 and folic acid. either use sublingual methylcobalamin and methyl folate or don’t do the study. i guess the real agenda was to scare the people with kidney disease away from supplements.

  • Paullet Hinton

    I’m on metanx with stage three kidney disease will that damage the kidneys more

    • tuyo101

      Me too! And waiting for the response. Will see my nephrologist in January and see what he says then report.