September 28, 2015
Popeye, mānuka, and keeping healthy
- Good story in the Herald: A survey from Southern Cross Health Insurance estimates that about 750,000 people in NZ regularly take vitamins and dietary supplements. Contrary to what some supporters say, there have been quite a lot of randomised trials of vitamin supplements — it’s just that they tend to give disappointing results. There are a few exceptions (such as folate in pregnancy) and a few arguably open questions (such as higher-dose vitamin D) but not many.
- Entertaining legal report in NBR: NZ Honey is fighting the Ministry for Primary Industries over whether it makes unsupported health claims for mānuka honey. The fun part is that the controversy isn’t whether there’s evidence for health benefits, it’s over whether brand names such as “Manuka Doctor” and “Manuka Pharm” are so clearly just puffery that no-one would mistake them for health claims
- People often claim spinach is very high in iron. Other people often claim this is due to a misplaced decimal point in early German research, and that Popeye didn’t know what he was talking about and spinach is a terrible source of iron. Still other people look into this more carefully and find that the error was not German, or a misplaced decimal point, and that Popeye’s health claims weren’t iron-related. In the end, spinach actually is a moderately good source of iron. (Karl Kruszelnicki, ABC Science)
Thomas Lumley (@tslumley) is Professor of Biostatistics at the University of Auckland. His research interests include semiparametric models, survey sampling, statistical computing, foundations of statistics, and whatever methodological problems his medical collaborators come up with. He also blogs at Biased and Inefficient See all posts by Thomas Lumley »
Vitamins are tricky, as it is quite clear that a deficiency can lead to poor health outcomes, as this is how we first discovered a bunch of them. On the other hand, even ones that you would think would be easy to take too little of (e.g. Vitamin C) are often taken in abundance.
I often wonder if the issue is not an non-linear curve being interpreted as linear (more is always better). Between 0 mg/day and the RDA, Vitamin C has positive effects. Above the RDA, it likely has little to no benefit (and may even become harmful). It was notable to me that one of the only recent vitamin trials to show any benefit was a multi-vitamin:
http://jama.jamanetwork.com/article.aspx?articleid=1380451
My conjecture is that people may have small deficiencies based on diet, and that a broad spectrum multi-vitamin can do little harm if you are worried that your diet isn’t optimal (living on Ramen noodles and peanut butter sandwiches, for example).
Basic sufficiency, on the other hand, fits the biological model really well. it’s absolutely clear that insufficient amounts of food are bad for people (I think this evidence is strong enough that trials are not needed — based on famines alone). But more is not always better when it comes to food (obesity is better than starvation but not a health promoting state).
All of this is a long winded way of saying that the problem likely depends on how which supplements people are taking. If a lot of people take a broad spectrum multi-vitamin every day or so then I am unsure that we have problem. If mega-doses of vitamin C and E are being taken, that would be of much greater concern.
9 years ago
When getting involved with a food frequency questionnaire with a nutritionist, I asked why they collected data on food supplements but didn’t include the data in the analyses. Her response was that most supplements don’t actually contain the ingredients or the amount of ingredients they are supposed to and they are in a form that gets excreted before the body can use them. From memory, her statements were based on a chemical analysis study of selected supplements.
Food supplements come under food laws rather than pharmaceutical laws so the have a lot of latitude.
9 years ago
Interesting, Megan. I do a lot of FFQ work in one of the NHLBI studies and we always sum the dietary and supplemental values for things like vitamin D and calcium (to pick some random examples).
So practices definitely vary
9 years ago