Wednesday, February 2, 2011

Vegetable vs. Animal Sources of Vitamin A: Why Eating Carrots Isn't Enough

Think you're getting enough vitamin A from carrots? Think again.
Think you're getting enough vitamin A from carrots? Think again. (Photo by Ben Hussman)

In the comment section of my previous post on genes, diet and cavities, a couple of readers commented that vitamin A is necessary for proper dental health. I replied that I get plenty of beta-carotene (the vitamin A precursor found in vegetables and fruits) from red palm oil, which I use for most of my cooking these days.

Today, however, I came across a couple of papers looking at how well humans actually absorb beta-carotene and convert it to vitamin A (link, link). To my surprise, the conversion rate was much poorer than I'd previously thought. The first paper, which looked at beta-carotene absorption in 11 men, had this to say:

The vitamin A activity of ß-carotene is variable. The carotene in fruit, grains, and oils seems to be more effective as a source of vitamin A than that in dark-green leafy vegetables.

So, not all sources of beta-carotene are equally good in terms of absorption. The conversion rate also depends on the amount of beta-carotene (the higher the amount, the lower the rate) and whether fat is included or not.

Strikingly, only 6 of the 11 men included in the study absorbed and converted the beta-carotene they were given. The remaining 5 were classified as non-responders. The authors conclude that the vitamin A activity of beta-carotene can be "surprisingly low and variable". Even in those who did respond to supplementation, mean absorption was only ~4% and the conversion ratio was ~0.05.

In a similar study on 11 women, the same thing happened: only 6 of the women absorbed and converted beta-carotene enough to be measurable, while 5 women were non-responders. In those who did respond, mean absorption was ~6% and the conversion ratio ~0.1. This confirms earlier findings reporting that women absorb and convert beta-carotene more efficiently than men; the same also appears to be true in rats.

These figures suggest that the commonly accepted conversion rates of beta-carotene from plant sources may be too optimistic. Even red palm oil might not be up to par with animal sources. In one study, switching from green leafy vegetables to red palm oil did increase retinol levels, but only in subjects who were vitamin A deficient to begin with (link). And for many Westerners who don't eat palm oil or organ meats, the reality is even worse:

Also, it seems that the vitamin A activity of ß-carotene that is not dissolved in oil and emulsified is low and variable. Most ß-carotene in the American diet is not consumed in an emulsified form with fat. Our intent was to replicate a typical diet to develop better leads for how the body utilizes its given resources. The fat content of the meal that accompanied the doses in our study was the recommended amount, 30%. Many professionals recommend lower-fat diets.

Now there's something for the low-fat raw food vegetarians to chew on. On the other hand, the absorption of retinol, found in animal sources such as liver and eggs, appears to be much higher. Most of the estimates I've seen on various websites are between 60-90%, but even that may be too conservative, as the only actual study I could find showed that absorption was >99% (link).

Since my vitamin D levels are already good, and I take vitamin K2 supplements, the missing link in the trinity of dental health could indeed be vitamin A in my case. While I do eat eggs every now and then, their retinol content is only about 10% of that of liver. I guess it's time to put organs on the menu.

For more information dental health, see these posts:

Genes, Diet and Oral Health: Why Do Some People Get Cavities and Others Don't?
Tea, Coffee and Cocoa: All Good for Your Teeth
Dental Health Effects of Green and Black Tea
Preventing Mouth Ulcers with Tea Tree Oil Toothpaste - Results after Two Months

Digg Technorati Stumbleupon Reddit Blinklist Furl Yahoo

9 kommenttia:

Anonymous February 5, 2011 at 5:01 AM  

Very interesting about the "non-responders" who didn't covert beta-carotene at all. Christopher Masterjohn has written some great articles on the synergy between vitamins A & D. I reference a number of them in this post if you're interested.

Riles February 7, 2011 at 2:19 AM  

Any opinions on this article?

Amy March 16, 2011 at 2:29 PM  

I haven't read all of the articles you linked to, so forgive me if you've covered this elsewhere:

Have you ever tried using xylitol? It is a natural sugar alcohol that is made from birch bark. It has been shown to kill the bacteria responsible for cavities, streptococcus mutans, and to alkalize the pH of saliva, (acidity in the mouth promotes tooth decay), helping teeth to absorb calcium from saliva so that they can remineralize.

Consuming 6-10 grams of xylitol a day, spread throughout the day is ideal (more than that amount doesn't increase effectiveness). You can find it in gum, candies or in granular form. Granular is cheapest, and provides 4 grams of xylitol per teaspoon. I think it tastes pretty much like sugar.

I have been using Dr. Ellie's system for about a month now (using generic versions of fluoride rinse and Listerine, even though she doesn't recommend that), and I've noticed a big difference in the amount of plaque (by-product of bacteria) in my mouth (virtually none now). I think the xylitol is the biggest factor in this. But the other steps are helpful if you have damaged teeth you are wanting to remineralize.

here is an article about a study done in Belize on the effect of xylitol on children's cavities

an article about a Swedish study

Good luck on your quest for healthier teeth!

JLL March 16, 2011 at 3:36 PM  


I haven't covered xylitol yet, but I'm planning on doing a post on it :) I already ordered a bag of xylitol powder from iHerb, we'll see if it helps. Thanks for the comment!


clare April 1, 2011 at 1:35 AM  

You have a fab blog..look forward to reading through it.

My teeth had been aching in one place for about a year then last yeah..bang..receding gums in one area :(

I had been using non fluoride toothpaste for a few yrs (the ones you get in herbal shops etc).

I was also using Squigle xylitol chewing gum and then found out they do a toothpaste called tooth builder which I now use with a tiny little squidge of their enamel saver toothpaste (enamel saver conains fluoride so dont want to use too much).

Does the trick for me, It may also be to with other ingredients in the paste though, not just the xylitol.

Againsthegrain April 13, 2011 at 7:13 PM  

I think people greatly overestimate how much beta-carotene is converted to true Vitamin A in the body.

Before I started taking thyroid hormone for hypothyroidism a few years ago, the palms of my hands were very ruddy colored, though I didn't think much of it. The ruddiness was gone a few months after starting thyroid hormone and hasn't returned. I think the color was from unconverted beta-carotenes that had built up. Now I make sure to eat vitamin A-rich grassfed butter, pasture egg yolks, and a bit of liver paté on a regular basis instead of relying on Vitamin A precursors from plant sources (I still eat some orange veggies, though).

Babies and young children aren't good converters, either. When my niece was a baby she really liked the sweeter orange vegetables, such as carrots, sweet potatoes, squashes, and the green veggies, well, not so much. So guess what, she was served a lot of sweet orange veggies. For quite a while she had an orange tinge to her fair complexion. We jokingly called her the "orange baby". She lost the tinge when she graduated from jarred baby foods and wasn't eating so much orange veggies.

In the local "natural" food store, I often see customers with a cart that contains a 25 pound bag or two of carrots. I can only assume they are making and consuming a LOT of carrot juice. At first glance, most of these people look like they are sporting a deep tan (this is in So Cal afterall), but a lingering look shows that their skin really has an orange cast, not a brown tan tone. Could be a bad fake tan, I suppose, but could every single person I've seen with 25 pound bags of carrots be orange due to fake tan products?

JLL May 26, 2011 at 10:10 AM  


Thanks for the tip, I may have to try that one out myself. Based on the comments at Amazon it's supposed to grow back the lost gingival tissue, unlike most other toothpastes which just numb the nerves. I've been looking for something like that.


Unknown June 22, 2013 at 5:28 AM  

But us vegetarians who eat a normal amount of fat and have a balance between cooked and raw foods are fine, right?

JLL June 25, 2013 at 11:47 AM  

@Mykell Miller,

I doubt it, if you're looking for optimal nutrition.


  © Blogger template 'Perfection' by 2008

Back to TOP