Doctor's Note

More on how phytonutrients in plant foods keep us healthy:

And on the mighty flavonoid family of phytonutrients:

And check out my other videos on greens.

For more context, check out my associated blog posts: Breast Cancer Stem Cells vs. Broccoli and Fighting Inflammation with Food Synergy.

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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 greens. Also, there are 1,449 other subjects covered in the rest of my videos–please feel free to explore them as well!

  • Joel

    Re: “…from a cancer perspective, smoking a single joint is equivalent to smoking an entire pack of cigarettes.”

    I was under the impression this alleged “equivalence” was disproven by Dr Donald Tashkin at UCLA and corroborated by others. Do you know of a study that refutes/disproves Dr Tashkin’s, which is a little older than 5 years (I saw something go by quickly on your video, too quickly to comprehend for me):

    Study Finds No Cancer-Marijuana Connection
    By Marc Kaufman
    Washington Post Staff Writer
    Friday, May 26, 2006; A03

    The largest study of its kind has unexpectedly concluded that smoking marijuana, even regularly and heavily, does not lead to lung cancer.
    The new findings “were against our expectations,” said Donald Tashkin of the University of California at Los Angeles, a pulmonologist who has studied marijuana for 30 years.
    “We hypothesized that there would be a positive association between marijuana use and lung cancer, and that the association would be more positive with heavier use,” he said. “What we found instead was no association at all, and even a suggestion of some protective effect.”
    Federal health and drug enforcement officials have widely used Tashkin’s previous work on marijuana to make the case that the drug is dangerous. Tashkin said that while he still believes marijuana is potentially harmful, its cancer-causing effects appear to be of less concern than previously thought.
    Earlier work established that marijuana does contain cancer-causing chemicals as potentially harmful as those in tobacco, he said. However, marijuana also contains the chemical THC, which he said may kill aging cells and keep them from becoming cancerous.
    Tashkin’s study, funded by the National Institutes of Health’s National Institute on Drug Abuse, involved 1,200 people in Los Angeles who had lung, neck or head cancer and an additional 1,040 people without cancer matched by age, sex and neighborhood.
    They were all asked about their lifetime use of marijuana, tobacco and alcohol. The heaviest marijuana smokers had lighted up more than 22,000 times, while moderately heavy usage was defined as smoking 11,000 to 22,000 marijuana cigarettes. Tashkin found that even the very heavy marijuana smokers showed no increased incidence of the three cancers studied.
    “This is the largest case-control study ever done, and everyone had to fill out a very extensive questionnaire about marijuana use,” he said. “Bias can creep into any research, but we controlled for as many confounding factors as we could, and so I believe these results have real meaning.”
    Tashkin’s group at the David Geffen School of Medicine at UCLA had hypothesized that marijuana would raise the risk of cancer on the basis of earlier small human studies, lab studies of animals, and the fact that marijuana users inhale more deeply and generally hold smoke in their lungs longer than tobacco smokers — exposing them to the dangerous chemicals for a longer time. In addition, Tashkin said, previous studies found that marijuana tar has 50 percent higher concentrations of chemicals linked to cancer than tobacco cigarette tar.
    While no association between marijuana smoking and cancer was found, the study findings, presented to the American Thoracic Society International Conference this week, did find a 20-fold increase in lung cancer among people who smoked two or more packs of cigarettes a day.
    The study was limited to people younger than 60 because those older than that were generally not exposed to marijuana in their youth, when it is most often tried.

    © 2006 The Washington Post Company

    • Michael Greger M.D.

      In terms of the purported link between smoking cannabis and lung cancer, although doubts have been raised, the latest review continues to raise strong concerns. It seems smoke inhalation is not good for your lungs, whether from a burning building or bogie.

      • silver17601

        Should we assume then, that if one vaporizes cannabis instead of smoking it, one can benefit from the many medicinal properties without cancer risk?

        • taha

          Yeah, I agree smoking (burning) cannabis comes along with a lot of toxins. I haven’t found any studies on vaporised cannabis, but I think it’s at least a lot less harmful than burning the cannabis.

  • LynnCS

    I noticed that Pine Needles in a tea is a good antioxidant. I am wondering if needles from a Douglas Fir or redwood would have the same properties. I am Raw Vegan and always interested in the options.

    • Michael Greger M.D.

      Pine needles have so much vitamin C that pine needle tea has been used with great success historically as a cure for scurvy. On the other hand there have been toxins found in the needles of some pines, so I would recommend sticking to more conventional dark green leafy leaves. If you want to be more adventurous, though, then the best resource I’m aware of is From Crabgrass Muffins to Pine Needle Tea by Linda Runyon.

      • LynnCS

        Thanks, Dr. Greger. I figured as much and have lots of options, especially now that I’ve upgraded to McDougalling. :-)

    • DStack

      I realize this is a minor point, but I don’t really understand some of the customs of raw diets. Doesn’t steeping the needles in hot water basically equate to cooking them? Why is that different for you?

      • LynnCS

        I eventually didn’t do well on the all raw diet. I am on the Starch Solution and will be for the rest of my life. Check it out.

  • Joel

    Re Dr Greger’s Oct 27, 2011 reply, the ‘latest review’ he cites states, “there is an emerging concern among many chest physicians who would suggest that habitual smoking of cannabis may contribute to the development of chronic obstructive pulmonary disease.”
“EMERGING CONCERN”, “SUGGEST” and “MAY” do not in my opinion imply “strong concerns”.

    This one was ignored:, which raises doubts about the so-called “strong concerns.”
    “It has often been assumed that smoking cannabis will have similar long-term effects to smoking tobacco. Several recent observational studies suggest that this is not the case…The evidence that smoking cannabis leads to features of chronic obstructive pulmonary disease, such as airflow obstruction and emphysema is not convincing. However, there are numerous case reports of bullous emphysema among cannabis smokers. These findings have not been confirmed in systematic analytical studies and probably represent uncommon adverse effects in very heavy cannabis smokers. There is now additional controversial evidence that cannabis is at least an occasional cause of respiratory malignancies, but again the evidence is inconclusive.

    How can 
“…not convincing… 
These findings have not been confirmed in systematic analytical studies and probably represent uncommon adverse effects…,” or 
“the evidence is inconclusive.”
be equated to “strong concerns?

    “evidence…not convincing”
“findings…not been confirmed”
“uncommon adverse effects”
    “the evidence is inconclusive.”

    I do not see a case for “strong concern”, certainly not in these phrases by the researchers themselves.

    Another example is the phrase, “the latest review”, which disingenuously implies it is the only review.

    There is also no mention of alternate forms of ingestion, such as vaporized cannabis (no smoke) or eating of cannabis, which reduce or eliminate lung impact altogether.

    The Tashkin study should be taken seriously. The man is a highly esteemed, long-time pulmonary researcher and many controls were built in to the study. I am aware of no followup studies that refute his findings; neither do I see any mentioned here since I asked that very question in my Sept 30, 2011 post. Another reason to review the Tashkin study is that there are studies done since then which strongly suggest cannabis actually fights cancer. I haven’t seen that information in my local newspaper; Dr Tashkin alluded to the possibility over 5 years ago when summarizing his findings.

    • Lisa

      Oops, voted Joel’s comment up in error; thought it was an arrow to
      expand comments. So, two years late and without getting hyper-analytical, when I read what Dr. Greger (and even what you, Joel) posted, personally,
      I see several caveats that shouldn’t be ignored. Not to mention, when I see the resin that coats pot smoking paraphernalia, common sense tells me it doesn’t belong in the lungs.

      • jazzfeed

        Good observation, yet what the BODY does with that residual is unknown, at least to me. In any case, how the body deals with it will not be the same as how inert nonporous glass deals with it. All this implies to me that further studies should be done on alternate methods of ingestion, as suggested by taha and silver17601. The temperature difference between vaporization and combustion, I believe, could be as great as 900 degrees, i.e., vapor: 300-400 degrees, burning: 1000-1200 degrees. In other words, given these figures which I believe are in the ball park, vaporization takes place at a 2.5 to 4 times lower temperature than combustion.

  • Francis Lingel

    I,ve heard that dandylyn isoneof 5 healthyest foods.  Do you have info?

  • Michael Greger M.D.

    For some context, please also check out my associated blog post Breast Cancer Stem Cells vs. Broccoli!

  • Michael Greger M.D.

    Please also check out my associated blog post Fighting Inflammation with Food Synergy

  • Sandy

    Should vegetables be consumed raw or cooked, to attain the greatest health benefit?

  • N_

    What do you say about hemp seeds?

  • Mirko
  • Oemba Doemba

    How is it possible that we get cancer and we can get prevention so easily by diet?

  • Wade Patton

    Dandelion greens (and flowers) are good this time of year.

  • Wade Patton

    From the National Cancer Institute, at the National Institutes of Health

    “Antitumor Effects

    One study in mice and rats suggested that cannabinoids may have a protective effect against the development of certain types of tumors.[3] During this 2-year study, groups of mice and rats were given various doses of THC by gavage. A dose-related decrease in the incidence of hepatic adenoma tumors and hepatocellular carcinoma (HCC) was observed in the mice. Decreased incidences of benign tumors (polyps and adenomas) in other organs (mammary gland, uterus, pituitary, testis, and pancreas)
    were also noted in the rats. In another study, delta-9-THC,
    delta-8-THC, and cannabinol were found to inhibit the growth of Lewis lung adenocarcinoma cells in vitro and in vivo .[4] In addition, other tumors have been shown to be sensitive to cannabinoid-induced growth inhibition.[5-8]…”

  • Wade Patton

    From Medical News Today, 14 July 2014

    “Further evidence that cannabis reduces tumor growth in new study”

  • Wade Patton

    The “one joint is a pack of cigarettes” junk is very old and tired. Please see links below.

  • Ras Bongo Natty Tafari

    Doc…I see you promote soy milk but I’ve hearing about its effect on the thyroid. Can you clarify?

  • lu

    I’ve read on some websites that greens provide vitamin d but couldn’t find this anywhere else. Could they just be referring to algae?

  • LOL!

    Greger, i love you, but i can’t let you go around having this miss information about cannabis among all this accurate information. It just muddles the water. The studies are clear, even insurance companies have decided to move cannabis smokers(non tobacco user) into the non smokers category and the non smokers rate. Every insurance company in the world would love to continue to this miss information on cannabis being as bad as tobacco, but it’s just not true.

    I love you Greger, please, you know in your heart what you must do. Redo the video and apologize for presenting a debunked study and continuing the cannabis propaganda which only became illegal for racist reasons.