Evidence Of Lutein Benefits Grows, But Too Early To Set RDI
This article was originally published in The Tan Sheet
The supplement industry’s interest in setting a recommended daily intake value for lutein intensifies as the scientific evidence grows linking the nutrient to ocular and cognitive health.
A lutein researcher says the industry will have to wait. The scientific community is not on the same page as the supplement industry, but it is getting closer, says Elizabeth Johnson, of Tufts University.
“We should begin that conversation,” Johnson said Oct. 19 during a science workshop at the Council for Responsible Nutrition Conference.
She acknowledged a lot of completed and ongoing research on lutein.
“Supplementation with lutein has been found to improve visual function under disability glare and photostress and it has been found to improve visual acuity in people with age-related macular degeneration,” the leading cause of blindness in older people, and those with cataracts, she said.
But, she added, scientists still must fill many gaps on how the body absorbs and uses lutein and how much the body needs during different phases of development.
Well-Established Benefits
The benefits on ocular health from lutein and zeaxanthin, the two carotenoids in the human eye, are perhaps the most well-established, said Johnson, who works in the carotenoids and health laboratory at the Jean Mayer U.S. Department of Agriculture Human Nutrition Research Center on Aging at Tufts.
For example, one observational study found a high daily intake of lutein and zeaxanthin reduced the risk of cataracts 18% in women who participated in a 10-year study (Also see "Researchers Eye Lutein, Zeaxanthin, Vitamin E To Reduce Cataracts" - Pink Sheet, 21 Jan, 2008.).
Other studies, including work by Johnson, show the carotenoids reduce the risk of AMD by shielding the eye from harmful blue light and possibly prevent oxidizing damage (Also see "Carotenoids, Anitoxidants Improve Treatment For AMD – Study" - Pink Sheet, 18 Feb, 2008.).
The link between lutein and zeaxanthin and AMD is important because there is no cure for the condition. This is one reason the supplement industry wants to establish an RDI to help prevent the disease and slow its progress.
Emerging Cognitive Link
Emerging science also links the carotenoids to cognitive and neural health, Johnson said.
Recent research by Johnson and others on lutein’s and zeaxanthin’s influence on cognitive function reveals daily supplementation of 12 mg of lutein and 800 mg of docosahexaenoic omega-3 acid daily for four months was associated with a significant increase in verbal fluency, learning and short-term memory in healthy women aged 60 to 80 years.
Scientists do not fully know how age influences lutein needs and how increased consumption would affect the uptake of other carotenoids and the functions they influence. – Elizabeth Johnson, Tufts University
Separately, the Georgia Centenarian Study of 49 people who lived to be older than 98 years, and whose brains were donated for research, revealed lower brain lutein levels were related to poor global cognition, executive function, recognition and mild cognitive impairment.
Establishing The Recommended Daily Intake
Despite these research results, Johnson hesitated to recommend an RDI value for “vitamin L.”
She explained scientists still do not fully know how age influences lutein needs and how increased lutein consumption would affect the uptake of other carotenoids and the functions they influence.
When pressed at CRN’s event in Rancho Palos Verdes, Calif., about a potential daily recommendation, Johnson acknowledged about 6 mg a day can prevent or slow AMD, and most people consume about 2 mg.
“There really is a gap between what we think is protective and what is not,” Johnson said.
However, she noted the “standard of care” for lutein supplementation may change depending on the results of the ongoing Age-Related Eye Disease Study II, a phase III clinical trial to test the impact on AMD of daily supplementation of 10 mg lutein, 2 mg zeaxanthin and 1 g EPA/DHA in addition to the antioxidants tested in AREDS I (Also see "NIH lutein study" - Pink Sheet, 9 Jan, 2006.).
If the AREDS II results are positive, 10 mg of lutein and 2 mg zeaxanthin likely will become the standard of care, she noted.
Johnson discourages taking a dose that is higher than a dietary level because the toxicity and side effects from high doses of lutein are unknown.
She said lower doses are safer also because “we have other carotenoids and when you are overdoing it on one, you are probably monopolizing the absorption and transport of the other carotenoids which have an important role in health as well.”
She added, more evidence on the nutrient’s influence on neural development is necessary before a substantial cognitive link is made and used as the basis for an RDI.