Durk Pearson & Sandy Shaw®

Higher Doses of Beta Carotene?

espite a long history of research recognizing that vitamins E and C work together for optimal health, some researchers remain unaware of this fact. However, there has been less appreciation given to the dependency of beta carotene on other antioxidants. Only when beta carotene is consumed together with adequate amounts of other antioxidants can its inherent utility be achieved. For some time, it seemed that beta carotene was of universal benefit with epidemiologic studies indicating broad benefits for cardiovascular disease and many kinds of cancer. However, it was also recognized that beta carotene could be acting as a marker for other nutrients found in fruits and vegetables. Unfortunately in the last few years, a number of studies and in particular a Finnish study (called the ATBC study which examines the use of beta carotene on smokers) have been published which found apparent harmful effects of beta carotene in smokers, and the results have been perplexing to much of the public. Scientists Durk Pearson and Sandy Shaw make the case for the use of beta carotene, not as a single nutrient but instead as an important part of a formulation complex of supporting nutrients designed to enhance the synergy of their coactivity in the war against promiscuous oxidative free radical damage.


WILL: Why does beta carotene seem to have chameleon-like properties?

DURK: Beta carotene is a good singlet oxygen quencher but it is not necessarily a good antioxidant. One of the things that we understood from food technology is that beta carotene is not like a normal antioxidant. In fact, at the high pressures of oxygen that occur in lung tissues, beta carotene can act as a pro-oxidant. It quenches (disarms) singlet oxygen, a highly reactive and toxic intermediate which may play a role in photo-induced aging. Beta carotene performs this function in plants, and can be useful similarly in human beings, also. It acts as a photo desensitizer, and in fact, it is used by people who have a photosensitivity condition called xeroderma pigmentosum.

SANDY: Plants use it as a protectant against photosensitization. They have to be sensitive to light because of the function of chlorophyll, but then they have carotenoids like beta carotene to protect against the damage that would be caused by singlet oxygen and other factors as a result of photosensitization.

DURK: If you have a plant that contains beta carotene, but it's a mutant and it has no chlorophyll, light won't hurt it. Light won't give it photosynthetic energy, but light won't burn it up either. If you have a plant that has neither beta carotene nor chlorophyll, it can be damaged by light. But it is not killed by relatively small amounts of light. On the other hand, if you have a plant that has chlorophyll but not the beta carotene, relatively small amounts of light are deadly; because you get singlet oxygen produced as a toxic bi-product of the photosynthetic reaction. Without the beta carotene around to quench singlet oxygen, plants end up dying. Beta carotene, at low pressures of oxygen in the presence of vitamin E - especially if you have some ascorbyl palmitate present - can act as a good antioxidant. And beta carotene's pro-oxidant properties at relatively normal pressures of oxygen can be significantly controlled and even reversed into an antioxidant effect with relatively large amounts of vitamin E.


Ascorbyl palmitate is a really potent
antioxidant synergist; especially
in the presence of vitamin E.

SANDY: However, there is no one-size fits all nutritional map. Some people are going to want more of a particular antioxidant, like vitamin C or beta carotene, than others.

DURK: You really need to give people flexibility in adjusting the particular ratios of what they're taking in specific amounts.

However as a cautionary note, beta carotene shouldn't be used by people who have liver damage or who are alcoholic. This conclusion, in part, was drawn from an experiment on baboons. They were getting 60% of their calories in the form of alcohol, which is truly humongous. The researchers found that giving the baboons a lot of beta carotene - I think it was 1/4 million IU of beta carotene per day - caused an increase in liver enzymes, suggesting liver damage.

SANDY: People who are heavy drinkers already, have an awful lot of problems with liver function. So it's not really that surprising that they're going to have trouble handling the normal nutrients that a non-drinking person or person who just drinks moderately might not have.


Beta carotene, at low pressures of oxygen
in the presence of vitamin E - especially
if you have some ascorbyl palmitate present -
can act as a good antioxidant.

DURK: In the presence of cigarette smoke in the lungs, beta carotene can be oxidized to an epoxide. The epoxide can increase the binding of the polynuclear aromatic hydrocarbon diolepoxides to the DNA, which can cause mutations that can lead to cancer.

SANDY: And it's well known that people who smoke have greatly reduced levels of antioxidants in the blood stream. This puts them at a disadvantage in handling a nutrient like beta carotene, which requires the presence of other antioxidants in order to prevent it from acting as a pro-oxidant.

DURK: We don't know how much antioxidant power, in the form of vitamin E, ascorbate, and ascorbyl palmitate, will protect the beta carotene from being converted to the epoxide in the presence of cigarette smoke. So it is better not to take any chances.

WILL: Despite the smoking brouhaha, isn't beta carotene useful for some cancers?

SANDY: Yes. It's known that beta carotene can protect against the development of certain kinds of cancers. For example, oral leukoplakia, which is a type of excessive cellular proliferation.

DURK: It's a pre-cancerous condition which can turn into cancer.

SANDY: Exactly. And beta carotene can regress that back to normal. So it is known that beta carotene can protect against the development of certain types of cancer. But as it turned out, people who smoke - and especially those who smoke and drink heavily - did not get protection against lung cancer with beta carotene. In fact, they were at a higher risk level.

WILL: During our conversation, I've brought up the figures from the Journal of National Cancer Institute which makes references to the ATBC study.1 And out of the 29,000 men aged 50-69 years old who smoked 5 or more cigarettes daily, they were assigned to receive vitamin E (50 mg) or beta carotene (20 mg) or both or placebo daily for 5-8 years. As you remember, this study of smokers found a relationship between beta carotene and lung cancer; ie, there appeared to be a higher incidence of lung cancer among those subjects (the smokers) taking beta carotene.

DURK: Remember that in smokers vitamin C is dramatically reduced. You may end up requiring three times as much vitamin C to maintain the same serum levels in a smoker as in a non-smoker.

WILL: Neither of these studies had vitamin C in them as far as I can see.


It's known that beta carotene can protect
against the development of
certain kinds of cancers.

DURK: Nope, and they were smoking. The study also found that most of the increase in lung cancer was concentrated in people who both smoke and drink. And that, of course, puts an additional free radical load on the body. It may also change the metabolism of people as well.

Another point to make about the ATBC study is: it was conducted in Finland where the amount of selenium - a very important mineral for antioxidant defense - in the diet has been notoriously low (in the hazardous range). Finnish health authorities now require that all fertilizer in Finland be supplemented with selenium. However, it's going to take a decade or two, maybe even three, before the soils really builds up to the point where they'll be getting, American mid-westerner level of selenium in their diet, let alone a supplemented level.

And if you consider people who are smoking and drinking, on a very low selenium diet and they don't receive additional vitamin C - the C is being destroyed by smoking and drinking - you end up with health problems such as cancer. Especially if there is beta carotene present. In effect, beta carotene increases the negative impact of smoking. Technically: beta carotene becomes oxidized to an epoxide which increases the carcinogenicity of the polynuclear aromatic hydrocarbons produced by smoking and its combustion tar metabolite diolepoxides. The beta carotene epoxide actually increases the way these carcinogens bind to the DNA.

WILL: Is there any possibility that malabsorption of beta carotene in the diet of subjects from Finland could have confounded the results to some degree, or was there significant genetic differences among the population?

DURK: That's purely speculative. One would hope that people from northern climates would have adjusted to absorb more beta carotene over the millennia and hold on to it longer. I was rather surprised at 20 mg a day how many people noticed a change in color of their skin (beta carotene affecting the pigment of skin). So it is also conceivable they might have greater absorption or retention. However, unless someone does some metastudy on beta carotene in subcutaneous fat in people's skins, I don't think we're going to know the answer to that one.

WILL: Nevertheless, Durk & Sandy, your points are clear. Beta carotene is an important nutrient but to gain its value, you must use it in conjunction with a complex of other antioxidants and particularly vitamin C and vitamin E.

Reference

  1. Albanes D, et al. Alpha-Tocopherol and beta-carotene supplements and lung cancer incidence in the alpha-tocopherol, beta-carotene cancer prevention study: effects of base-line characteristics and study compliance. J Natl Cancer Inst. 1996;88:1560-1570.

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