January 21, 2001

Carotenoids

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Carotenoids

A report on new information from the Gordon Research Conference
by Gislin Dagnelie, Ph.D.
January 21, 2001
Over the past week I attended the Gordon Research Conference (GRC) on carotenoids, a meeting that is held once per 3 years to exchange the most current information in the area of research on plant and animal substances that appear to play a role in protecting human tissues against the effects of light, free radicals, and other attacks by concentrated energy particles. Although the carotenoids that are best known and most important to us (beta-carotene, lutein, zeaxanthin, lycopene) are small in number, there are actually several hundred known carotenoids, and for many of them it is not known whether they play a specific role in the human body, alone or in combination, and to what extent their roles are interchangeable.
I learned a lot of things about carotenoids, some of which are highly specialized, such as biochemic reactions, plant genetics, salmon breeding data (the pink color in salmon is called by astaxanthin), etc., and part of which I would have a lot of trouble summarizing with any degee of precision. But I did learn a few things that should be of interest to those who have looked at either food-ingested or supplemented carotenoids as a possible ally in the fight for better vision and, hopefully, slowing down the degeneration process. Here are the most important ones:
1. Carotenoids require substantial amounts of dietary fat in order to be absorbed. A researcher from Ohio State showed that the same 8.5 oz (240 grams) mixed salad can yield none, a modest portion, or almost all of its carotenoids to the bloodstream of the person eating it, depending on the fat content of the salad dressing with which it was combined. (Nothing else was eaten within several hours to avoid the effects of other fat sources).
The surprising point was that the fat contents for the high and low-fat dressing were 28 and 6 grams, respectively, so that’s quite a lot. I asked her if she felt that the dressing could have been replaced by another source of fat (e.g. butter on bread, meat, fish, etc). She felt that this was almost certainly true, but noted that butter on bread would typically yield no more than a few grams of fat, and that very lean meat or fish might also fall short. A combination would be a good idea. Some supplements (e.g. lutein capsules, vitamin E) come with their own fat (oil beadlets used as a solvent, oil in a gelcap), so they are likely to get absorbed more easily. Even there, though, one would probably be much better of taking these supplements with a meal.
2. The theory that different carotenoids (beta-carotene or vitamin A and lutein) should be taken at separate meals to prevent competition in absorption by the body is probably incorrect. A study looking at combined intake of lycopene (either from tomatoes or as a supplement) and lutein (either from spinach or as a supplement) found that absorption of the combination was possibly even better than for the supplements separately. Again, this probably requires adequate amounts of fat being available as a solvent.
3. Betacarotene plays a somewhat unusual role. Ever since two studies, more than five years ago, found that it may, in fact, increase rather than reduce cancer risk (at least, it did so for lung cancer in a group of older male smokers in Finland), it has had a bit of a bad reputation. The current understanding is that betacarotene, when acting as an antioxidant, takes a chemical form that is quite aggressive (like any antioxidant itself gets oxidated in the reaction, and in turn will oxidate other molecules in order to regenerate, so does betacarotene, but apparently it is harsher than most), and it presumably requires the presence of other carotenoids (or other antioxidants such as vitamins C and E) to convert it into a more harmless form. For this reason, it is probably a good idea for those taking betacarotene supplements to combine it with vitamin E or C. On the other hand, the conversion process from betacarotene into vitamin A makes betacarotene a safer supplement than vitamin A itself. It is known that long-term high-dose vitamin A intake can be damaging to the liver, and presumably the vitamin A circulates in the blood for quite a while once it has been absorbed. It does not get excreted by the kidneys, or broken down easily. The conversion of betacarotene into vitamin A, on the other hand, is controlled by the concentration of vitamin A already present, and the excess betacarotene is excreted.
The conference attendees showed a lot of interest in the relatively recent results on possible benefits of carotenoids (esp. lutein and zeaxanthin) to the eyes; remember the last carotenoids GRC was three years ago, and most carotenoid researchers do not (or rather did not) follow the eye research literature, and elected John Landrum from the University of Miami, who has a long track record in the study of macular pigment and other possible roles for carotenoids in the retina, to be one of the two organizers for the next conference, three years from now. Let’s hope the retinal degeneration community will have a lot of new and exciting information to add by that time.
Gislin Dagnelie, Ph.D.
Assistant Professor of Ophthalmology
Lions Vision Research & Rehab Center

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