The web page at Kemin foods has reported:
"1994: Dr. Johanna Seddon of Harvard University published a study in the Journal of the American Medical Association that examined the effect of consumption of specific carotenoids on AMD prevalence. The study found that the highest correlation of disease prevention was associated with an intake of 6 mg per day of lutein, which led to a 43% lower prevalence of disease. The authors recommended a diet high in lutein to lower the risk of contracting AMD."(Note that estimates are half of people over 75 are at risk for macular degeneration or "AMD".)
It is easy to infer from this that higher amounts than 6 mg would lead to less then a 43% lower prevalence of macular degeneration since it clearly states "highest correlation of disease prevention" is the 6 mg per day intake.
What the study, published in the November 9th, 1994 issue of the JAMA, did say is that "There was a statistically significant, apparently linear trend for a reduction in risk for AMD with increasing amount of carotenoids in the food. ..., we estimated the risk for AMD to be reduced by 43% among people whose consumption of dietary carotenoids placed them in the highest quintile of dietary carotenoid intake compared with those in the lowest quintile." (Note that this leaves 57% of half the people over 75 still at risk.)
(This study obtained its data from questionaires filled out by participants who were asked to recall the frequency of consumption of each food item during the past year. Statistical methods were then used to determine results. This study did not quantitatively measure carotinoid intake and it did not measure blood serum levels.)
The conclusion this study makes is the higher the lutein intake the lower the risk for macular degeneration, up to the highest normal consumption of lutein that was estimated to be 6 mg/d. Higher levels were not included as part of the study, so it can say nothing about the OVERALL dose/response needed to obtain the "highest correlation of disease prevention" possible.
Studies at the USDA on a limited number of subjects using controlled lutein intake and measurement of blood lutein levels show 10 mg/day raised blood levels to the 50 ug/dl range and 20 mg/day to the 100 ug/ml range. This supports the principle of a linear dose/response as measured by blood plasma levels, but it unfortunately does not answer the question as to whether a similar reduction in risk results when taking the higher doses of lutein.
To date there is no controlled study of a statistically significant number of subjects over a sufficient time period to determine the "best" dosage of lutein for reducing risk of macular degeneration to the maximum degree possible, ideally a 100% risk reduction. The reasonable assumption is that the actual "highest correlation of disease prevention" has not yet been determined but exists somewhere between 6 mg/day for a 43% reduction and more then 6mg/day amount for a highest risk reduction.
So what about the remaining 57% of the more than half of all people over 75 who are still at risk for macular degeneration even if they do intake 6 mg/day? Since it is known with a reasonable degree of reliability that plasma levels are dose responsive up to the 20 mg/day dose, a reasonable assumption exists that the 20 mg/day dose could yield a higher percentage of risk reduction.
Additionally there is the question of macular degeneration already having set in. The above considerations only involve prevention in normal healthy eyes as related to dietary factors, and the Seddon study only addressed prevention in that context. If macular degradation has set in that implies, along with inadequate dietary factors, a physiological or genetic vulnerability to macular degeneration since a large portion of people in the risk group in fact never experience macular degeneration. To date there are some reports such as the Richer study presented at the Southern Council of Optomitrists 1999 annual meeting that support lutein as being therapeutic, but no large controlled study of a significant number of subjects to confirm lutein as an effective and reliable therapeutic agent for post onset macular degeneration. And again what is left is only a reasonable assumption relating limited studies and anecdotal reports to the relationship of lutein to therapeutic effectiveness.
But if the choice is 6 mg/day or 20 mg/day, that reasonable assumption supports 20mg providing a better safety net.
Note that a certain vitamin/supplement maker who shall remain nameless but not initial-less is advertising LUTEIN, good for your eyes, now in their multi-vitamins. But what C fails to mention is the amount they put in, 250 mcg, is far short of even the 6 mg supplements many retailers are selling (based on the previously mentioned 1994 Seddon study).
Since 1 mcg (microgram)= .001 mg (milligram)
and therefore 250 mcg = .25 mg,
then 250 mcg is 1/24th of 6 mg and 1/80th of 20 mg.
Can this be considered a genuine benefit to the consumer, or is it more a marketing ploy based on consumer confusion about mcg vs mg and how much LUTEIN is realistically needed for meaningful risk reduction?
Note also that more expensive supplements consisting of zeaxanthin have become available based on studies that show it is present at the center of the macula in relevantly higher amounts that lutein.