Dispelling nutrition myths, ranting, and occasionally, raving


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Vitamin A and pregnancy

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A friend, and fellow RD, alerted me to a brief article on vitamin A and asthma recently. Good thing, because I really wasn’t sure what I was going to blog about. Sometimes I have a wealth of topics to cover and sometimes I’m desperate for something to rant about. While this article is a good thing for my blog it’s not such a good thing for the advancement of nutrition knowledge and supplements.

Of course, this article appeared on a supplement store page. Hopefully most readers would be savvy enough to do their own research, or at least consult with their doctor before deciding that it’s a brilliant idea to supplement with vitamin A during pregnancy to reduce the risk of their unborn child developing asthma later in life.

I found the research publication upon which the article was based. Um, you guys, check out the title of the paper: Prenatal retinoid deficiency leads to airway hyperresponsiveness in adult mice. That’s right, mice. You really want to start popping vitamin A pills during pregnancy on the basis of a mouse study?? It’s important to note that they were also comparing mice that were vitamin A deficient to mice that were supplemented to optimal levels of vitamin A. The study was considering populations in developing countries which are commonly vitamin A-deficient. Not our North American population which is very rarely vitamin A deficient (1).

The article does make an important point: “adverse fetal exposures that cause subtle changes in developing organs can have lifelong consequences.” Too bad they fail to mention that excessive consumption of vitamin A can be the cause of such developmental changes. Vitamin A supplementation during pregnancy has been linked to birth defects (2). Adequate amounts of vitamin A can be easily obtained through food. And, especially when taking a prenatal multivitamin, women are ill-advised to taken an additional vitamin A supplement. Please consult with your primary health care practitioner before taking any supplements. Especially when pregnant, as the consequences can affect more than just yourself.


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Vitamin A and Iron Absorption

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And this is a prime example of why 140 characters are not enough to provide nutrition counselling. It does appear that lower doses of vitamin A (such as the quantities you might obtain from eating the foods listed above) may increase absorption of non-heme iron (i.e. plant sources of iron). However, the increase seems to be minimal in comparison to consuming an iron supplement alone. In addition, when vitamin A supplements of 1, 800 µg were consumed with iron supplements they actually deceased iron absorption (1). Vitamin C, however, has been proven to increase iron absorption (2).

Lessons here:

1. Do your own research. It’s difficult for a 140 character tweet to convey sufficient information for you to make an informed dietary decision.

2. Try to get most of your nutrients from food, rather than supplements. While consuming foods that contain vitamin A may aid in iron absorption, consuming vitamin A supplements may actually decrease iron absorption.