Doctor's Note

For more on blue-green algae, check out these videos:
Diet and Amyotrophic Lateral Sclerosis (ALS)
Infant Seizures Linked to Mother’s Spirulina Use

Also, check out my other videos on blue-green algae. And note that chlorella is not in the same category as blue-green algae. 

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  • Michael Greger M.D.

    Please feel free to post any ask-the-doctor type questions here in the comments section and I’d be happy to try to answer them. And check out the other videos on blue-green algae. And note that chlorella is not in the same category as blue-green algae. Also, there are 1,449 other subjects covered in the rest of my videos–please feel free to explore them as well!

  • Becky

    I was wondering if you know anything about Carageenen from seaweed, so far I’ve read that it isn’t good to consume, however some vitamin supplements have it, is this such a small amount I shouldn’t worry? Sorry I wasn’t sure where to post this.

    • Michael Greger M.D.

      As a precautionary measure I would recommend those with inflammatory intestinal disorders try to stay away from it. Still unclear whether it should be avoided otherwise. I’ll keep an eye out for new research–thanks for your question!

  • Michael Greger M.D.

    For some context, please check out my associated blog post Multivitamins and Mortality!

  • I would with the wild blue green algae and ee are PROVEN to be BMAA free (is 3rd party). We are NSF certified, proving we are clear of all contaminants including microcystin

  • Sorry – that was strange.  I work with the wild blue green algae from Upper Klamath Lake. While there has been a lot of negative press our algae is safe. I have been eating it 25 years.
    1. We are PROVEN to be BMAA free (is 3rd party)
    2. We are not farmed, and we are organic, removing herbicide/pesticide issues
    3. We are NSF certified, proving we are clear of all contaminants including microcystin

  • Jesse

    so you say that we should all take 250 mg of algae based DHA everyday but stay away from spirulina, chlorella and blue green. what gives?

  • Francisco Carreño-Galvez

    I have researched regarding the blue-green algae Aphanizomenon Flos-Aquae (AFA), since I found it in the book “Healing with Whole Foods” (Paul Pitchford) and found out that there are certain studies with specific extracts that haven been proven to be toxin-free. So, since there are a huge number of benefits from using AFA (among other types of seaweed), WOULD YOU CONSIDER POSITIVE TO INCLUDE IT IN OUR PLANT-BASED DIET? (most like likely in form of extract) Thank you.

    • Karen

      Yes, please answer this question, Dr Greger. I stopped taking mine after reading your opinion of Spirulina, but my arthritis is getting worse since I stopped taking it.

      • Sam

        Take about 20 tablets of chlorella from Pukka (they are crasy about quality, use only organic cultivated under sun and check regularly) and after using it for about a month switch to wheat grass (also Pukka as their wheat grass powder is 30 x stronger than regular). Use chlorella alternativly with either wheat greas, Clean greens or other powders by Pukka:

  • Mc

    How do you feel about green powders such as amazing grass supplements and garden of life green blend powders? These contain blue green algae, but many other things as well.

  • steff

    Do you know anything about lithothamnion…algae from Iceland used for calcium in bone health supplements?

  • Abi

    Hello there! My vegan daughter’s favoured soya milk is calcium fortified with lithothamnium calcareum seaweed/algae. Is this a good and safe seaweed for us to be consuming?

    Many thanks.

  • Darryl

    Not just supplements. Bioaccumulations of BMAA have been found in seafood (especially shellfish) consumed by clusters of amyotrophic lateral sclerosis (ALS, Lou Gehrig’s disease) patients. Recent reviews:

    The emerging science of BMAA: do cyanobacteria contribute to neurodegenerative disease? (2012)
    Presence of the neurotoxin BMAA in aquatic ecosystems: What do we really know? (2014)
    β-N-methylamino-L-alanine (BMAA) produced by cyanobacteria as a possible cause of neurodegenerative deseases (2014)

    • This is totally off topic but… Somewhere in your 658 comments, you talk about the studies showing pescatarians have a slight advantage over vegans in mortality studies and why you think that is. Which mortality studies? Mind citing one or two? I’d like to have a read.

      • Darryl

        Those 2 comments are most likely referring to the early results through 2009 from Adventist Health Study 2, which is the first prospective study with enough vegans to provide any sort of statistically significant results for mortality. As of that report, vegans had an adjusted mortality rate 15% below that of omnivores, though still not quite achieving statistical significance. Pescetarians had a mortality rate 19% below that of omnivores, and because this is a larger cohort, had already achieved statistical significance. While pescetarians may appear to have a lower risk, the difference with vegans is nowhere near statistical significance (the two RR confidence intervals are 0.69-0.94 and 0.73-1.01), so there’s a very good possibility this distinction would arise by chance from sampling even if the two groups had identical risks.

        Curiously, vegan men had a statistically significant 28% lower mortality risk than omnivore men, and nearly identical to pescetarian men. Its the vegan women who don’t seem to be benefiting much, with a negligible 3% lower risk than omnivores, whereas the pescetarian women had a non-significant 12% lower risk. It should be noted that the comparison omnivores in AHS-2 are much healthier than the general population, as Adventists have low rates of smoking, alcohol use, and are more socially engaged.

        These results don’t say much at present about distinctions between vegan and pescetarian health risks, but I do think vegans should pay attention, in order to avoid complacency in our dietary and supplement strategies. Followup is continuing, and if AHS-1 (1/3rd as large, with few vegans) is a guide, AHS-2 may continue through 2016, with results published through the next decade.

        • And re: the comments comparing cancer risk in pescatarians versus vegans– What are those comments referring to?

          • Darryl

            Another report covered cancer incidence in the early years of AHS-2. Pescetarians lower trending adjusted hazard ratio of 0.88 (0.77–1.01) compared to omnivores, while vegans barely achieved statistical significance with 0.84 (0.72–0.99) – if the 95% confidence interval doesn’t include the reference group HR of 1.00, then its “significant”. As either confidence interval encompases the HR of the other group, there’s no significant difference between pescetarians and vegans in these results.

  • Lukas Klein

    Hi – I note that there is a discrepancy between the video and the transcript when it comes to chlorella – the former does not mention it, the transcript does. Do you / studies consider chlorella safe or not?

    • Alex

      I would like to know if chlorella is safe or not too. Would appreciate an answer. Thanks

  • Alex

    What are the common terms/labels that are considered blue-green algae? I understand that Spirulina is one of the blue-green algae, what are the others. Would appreciate if you could list down the all terms/text/labels that we see on the bottles/ingredients that is considered blue-green algae. Thanks.

  • precie

    Oh no I thought I heard from one of Dr. Greger’s vidoes to take microalgae. Now I’m confused.

    • Shaylen Snarski

      Some of his videos contradict themselves and I wish he’d elaborate as opposed to ignoring previous statements, it’s frustrating. I don’t know if this is the case here as I haven’t seen the other videos. Love Dr. Greger, but that is one thing I don’t like about some of his videos.

  • debabced

    Here is another ALS cluster study,, but these were Ashkenazi Jewish. This one here show a higher risk of ALS if Ashkenazi Jewish and family history of ALS. It says “Among relatives of Ashkenazi schizophrenic probands the rate of amyotrophic lateral sclerosis was 3/1,000, compared to expected population rates of approximately 2/100,000.” Someone said the one rate would have been an annual rate and the 2/100,000 is a lifetime rate, so I don’t think this is 150 times the risk, but more like 4 times the risk.