February 2, 2017

Eat more kale?

From the Mail, via the Herald

Eating nuts, kale and avocado could help protect women from suffering a miscarriage, new research suggests.

Being deficient in vitamin E starves an embryo of vital energy and nutrients it needs to grow, scientists have found.

There’s a sense in which this is true. But only a weak one.  Here’s the first sentence of the research paper (via Mark Hanna)

Vitamin E (α-tocopherol, VitE) was discovered in 1922 because it prevented embryonic mortality in rats, but the involved mechanisms remain unknown 

That is, it’s been known since vitamin E was discovered 95 years ago that severe deficiency causes miscarriage in rats. In fact, the chemical name ‘tocopherol’ comes from Greek words meaning, basically, “to carry a pregnancy.” This isn’t new.  The new research was a study of severe deficiency in little tropical fish, so it wouldn’t be an improvement over rats from the point of view of a public health message.  And the research paper doesn’t try to say anything about avocados and kale for preventing miscarriage; it’s about clarifying what goes wrong with the embryos at a biochemical level.

The dietary-advice question would be whether it’s common for women to have low enough levels of vitamin E to increase miscarriage risk, and if so whether nuts, kale, and avocado would help or whether supplements make sense as they do with folate and perhaps iodine.  Somewhat surprisingly, the first published research on this question seems to be from 2014 (story, paper).  In a study in rural Bangladesh, where nearly 75% of women had vitamin E deficiency, those with low vitamin E were twice as likely to miscarry.  I don’t have data for New Zealand, but in the US less than 1% of people have vitamin E deficiency of that severity.  It doesn’t look to be a big problem. And, from the authors of the 2014 study:

Schulze says that the study may not be generalizable to higher-income nations where women of childbearing age tend to have better nutritional status.

It’s possible that slight deficiency increases miscarriage risk slightly, but there isn’t any direct evidence. And the new research doesn’t even try to address this issue.

Finally, if someone wanted to get more vitamin E, would the recommendations help? Well, according to this site, it would take 14 cups of kale a day to get up to the recommended daily intake. And we know there are problems with avocado in younger adults. So perhaps try the nuts instead.


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 »