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VITAMIN A and BETA-CAROTENE and CARDIOVASCULAR DISEASE                            

Abstract: Research to date shows that Vitamin A in amounts up to about 5000 IU units used over periods of 7 or more years is an antioxidant that can reduce risk of heart disease about 25-30% for a added amount of about 3,000 IU per day.   Beta-carotene, the most popular source of Vitamin A in supplements is converted to Vitamin A by the body in variable amounts.  Life Ahead now assumes 3 IU of Beta carotene provides 1 IU of Vitamin A.  Because a typical US diet includes about 2,500 IU of Vitamin A,  use of a supplement of Vitamin A of about 3,000 IU or a supplement of Beta-carotene of 10,000 IU per day usually will be prudent.  Life Ahead credits modest benefits for Vitamin A from a total of food and supplements for amounts only up to 5,000 IU per day, and credits no benefits of the Vitamin for those that smoke cigarettes.  Higher amounts of Vitamin A than this are not useful and can be harmful.  Life Ahead also values Vitamin A as one of 4 antioxidants that in total have a limiting value.  Users should take Beta Carotene together with the other recommended three antioxidants for best assurance of antioxidant benefit.

Vitamin A designates a family of vitamins that are fat soluble. Retinol a most active agent of this family.  Carotenoids are Vitamins that are converted to Vitamin A by body chemistry.  Beta carotene is a carotenoid that is converted to Vitamin A efficiently and probably is the dietary factor and supplement most commonly taken by individuals. Values of agents related to Vitamin A can be quite confusing.   One basis is the retinol equivalent called the RE.  Most tables of Vitamin values in foods are expressed in IU units of Vitamin A.  One RE is 5 IU. But most research is related to Beta-carotene values, and most users take Vitamin A as Beta-carotene. And values of Beta-carotene differ substantially from those of Vitamin A per se.  The conversion ratios from IU of Beta-carotene to IU equivalents in Vitamin A differ from various sources from 2 to 1 to up to 6 to 1. Further confusing is that values of Beta-carotene are sometimes expressed in mg. rather than IU.  1 mg of Beta-carotene equals about 1600 IU.  It has been stated that the body converts Beta-carotene to Vitamin A only in amounts needed. Life Ahead assumes as approximation a conversion value of 3 to 1 for Beta-carotene to Vitamin A for both research and user values. 

The RDA or nutrition desired values for Vitamin A now are 5,000 IU for men and 4,000 IU for women. An average US intake of Vitamin A from foods is probably about 2,500 IU.  Life Ahead "Good" diet #2 includes 3600 IU, the "Poor" diet #3 includes 2200 IU of Vitamin A.  From this and results of various research studies it seems likely that rather few people today obtain enough Vitamin A from foods to meet the RDA values. Fruits and some vegetables, with carrots as of particular note are good sources of Vitamin A.  But the vitamin also is included in cereals and a very broad range of foods.

But the RDA values do not recognize the potential contribution of Vitamin A as an antioxidant that can reduce risk of cardiovascular diseases and cancer.  The key research found on dietary Vitamin A is included in Table B following. The average risk ratio for the 6 observation studies was 0.72 for an average of about 3,000 IU of Vitamin A per day.  The individual studies as usual have substantial margins of error, and all observation studies are statistically consistent with a risk of 0.7-0.75.  Thus the combination of results from the studies indicate a good likelihood that Vitamin A in these amounts can reduce risk of coronary disease modestly.. Values up to the RDA 5,000 for men and 4,000 for women should be a target for lowest cardiovascular risk as well as for good nutrition.

The fact that Vitamin A can reduce risk of heart disease is further confirmed by results from a number of studies reviewed but not included in Table B relating amounts of beta-carotene in blood to risk of disease.  These show that risk of heart disease is significantly reduced from higher amounts of carotenes in circulating blood.  Vitamin A probably produces its benefit as an antioxidant that slows atherosclerosis. This means that its benefit will depend on duration of use. This value from Studies 1 through 6 appears to be a risk factor of about 0.975-0.980 per year of exposure for 3,000 IU of Vitamin A.

A major problem in the health valuation of Beta-carotene has been results from clinical studies that found not only no benefit but even a  possibility of harm from excessive amounts of the Vitamin. These results are listed as Studies C1 through C4 in the Table B.  An evident problem in each of these studies was that they used enormous amounts of Beta-carotene, as more than ten times the typical amounts used in either the observation studies or is considered via the RDA.  Studies C3 and C4 were for smokers, and smoking can erase the benefit of antioxidants.  Studies C1, C3 and C4 were done for much too short a duration to measure the effect of Vitamin A as an antioxidant.  But on balance they suggest that the excessive amounts of Vitamin A used may have been the key factor responsible for their failure to find benefit.  This likelihood is indicated from the lack of benefit found from Study C that studied the effect of duration for periods up to 11 years. Study C3 found the extremely large amount of Vitamin used to be harmful with near statistical significance.  On balance it is felt that the results from these studies of very large amounts of Vitamin A are not pertinent to the value of Vitamin A in food plus supplements in the range of 5,000 IU equivalent or lower. 

Vitamin A in amounts much higher than this 5,000 IU can produce a substantial risk of osteoporosis and breaking of bones.  Vitamin A in amounts much larger than this also has been claimed to be toxic, causing nausea, vomiting, and joint pain. Research does not value supplement amounts above 5,000 IU as useful. Thus Life Ahead limits valuation of benefits of Vitamin A in foods plus supplements only to a maximum of 5000 IU and health-interested persons should avoid taking higher amounts than this.

Life Ahead does not value Vitamin A or Beta-carotene directly.  Rather it includes its contribution in combination with antioxidants with Vitamin C, E, and Selenium.  Vitamin A is valued at a lower contribution to antioxidant value than is Vitamin E.  A total dietary value of only up to 5,000 IU of Vitamin A is accepted in this total, and supplements of it are not credited with any value for those smoking cigarettes.  This is about the same amount that is suggested by the RDA.  See the Antioxidant Model.  Because most people will not obtain the desired 5,000 IU equivalent from their dietary foods, a Beta-carotene supplement of about 10,000 IU or a bit less will be a usually desirable for health-interested persons. Note these values and those of other supplements also are adjusted further for body weight and gender in Life Ahead's suggested targets.

                                                                                            Table B

EFFECT of BETA-CAROTENE and VITAMIN A on HEART DISEASE