Bye….Bye…Beta-carotene. Say hello to Lutein/zeaxanthine

It’s been a bad year for beta-carotene.

Beta-carotene was part of the AREDS I supplementation along with vitamins C, E, zinc, and copper. This combination reduced the progression to severe AMD by about 25% over five years. The dose of beta-carotene used in AREDS I was a whopping 15mg, about 28,000 IU per day and about six times the daily recommended value. The Physicians’ Health study however showed no difference in AMD between those taking a supplement of 50mg of beta-carotene every other day compared to those who did not.(1) This result was one of the reasons that the AREDS II trial includes a group that is randomized to no beta-carotene (see January 22, 2007 blog on AREDS II).

Now there is concern that extra beta-carotene might actually make AMD worse. Beta-carotene becomes vitamin A, or retinol, which is necessary for sight. In the outer segments of the cones and rods, all trans-retinol is converted to cis-retinol when exposed to light and this starts the electro-chemical process of seeing. If there is no vitamin A, there is no sight. The problem is that the eye doesn’t perfectly recycle the retinol. There are a variety of breakdown products, called retinoids, which accumulate in macular degeneration. One of the breakdown products, called A2E is considered to be especially toxic. There is one study that is testing a drug that binds to the same transport proteins that are used by retinol to get into the eye (see November 19, 2007 blog, Age Related Macular Degeneration: Treatments for Dry AMD). The idea is to prevent an excess of retinol in the eye which will limit the production of A2E and potentially other harmful retinoids. It is hoped that this will reduce the progression of AMD especially the dry or atrophic form. This is analogous to starving the eye a bit from retinol and is the exact opposite idea of supplementing with high doses of beta-carotene!

A recent study from Australia showed that dietary lutein and zeaxanthin reduced the risk of the development of AMD long-term.(2) The same study showed that a high intake of beta-carotene was associated with an increased risk of AMD.

A study from Italy in the same journal showed that short term supplementation with vitamin C, E, copper, zinc, lutein, zeaxanthin, and astaxanthin increased macular function as measured by a special test called a multifocal electroretinogram.(3) Notice that no beta-carotene was used in their patients.

I would recommend an AREDS supplement with lutein especially and also zeaxanthine if you can get it. The doses used in AREDS II are 10 mg lutein and 2mg zexanthine. Don’t take beta-carotene if you’re a smoker since it increases the risk of lung cancer. I would also limit or eliminate the amount of beta-carotene supplements even if you’re not a smoker.

Just eat your vegetables.

References:

1. Christen WG, Glynn RJ, Ajani UA, et al. Age-related maculopathy in a randomized trial of low-dose aspirin among US physicians. Arch Ophthalmol 2001; 119: 1143-9.

2. Tan, JSL, Wang, JJ, “Dietarty Antioxidants and the Long-term Incidence of Age-Related Macular Degeneration.” Ophthalmology 2008;115-334-341.

3. Parisi, V., Tedeschi, M, “Carotenoids and Antioxidants in Age-Related Maculopathy Italian Study.” Ophthalmology 2008;115:324-333.

How Safe is Fish?

Previous blogs have discussed the evidence that omega-3 polyunsaturated fatty acids may reduce the risk of heart disease and AMD.

• Lutein/zeaxanthin and Omega-3 poly-unsaturated fatty acids and AMD
• Dietary Fat and AMD
  
• The US Department of Agriculture (USDA) - Nutrient Database for Standard Reference
  

The Age-Related Eye Disease Study 2 (AREDS 2) is testing, among other things, whether supplementation with one gram of docosahexaenoic acid (DHA), one of the omega-3 fatty acids, per day reduces the progression of AMD. Recently there have been warnings that fish may be contaminated with mercury, dioxins, and polychlorinated biphenyls (PCBs). People with AMD, or at risk for AMD, may wonder if the benefit of eating fish outweighs the risk.

A recent article in JAMA evaluated all the articles that dealt with the benefit of eating fish along with the articles that dealt with its contamination. The article’s conclusion was that the benefit, (reducing the risk of coronary artery disease), outweighs the risks. They recommended that women of child-bearing age should also eat fish but avoid the species that have the highest concentrations of mercury.

In general, the highest mercury concentrations are found in long-living predator fish such as swordfish and shark and lower levels are found in shorter-living species such as shellfish and salmon. Oily fish with low levels of mercury may the best such as: sardines, herring, salmon, mussels, and oysters. The paper recommended though, that one should eat a variety of seafood.

We should remember that it hasn’t yet been proven that the intake of omega-3 polyunsaturated fatty acids reduces the risk of AMD. We also don’t know how much omega-3 is necessary although we believe that it’s a modest amount. Therefore, if you’re not too keen on seafood, eating it twice a week is probably plenty.

Reference:

Mozaffarian D, Rimm EB. Fish intake, contaminants, and human health: evaluating the risks and the benefits. JAMA. 2006 Oct 18;296(15):1885-99.