Can lutein & zeaxanthin improve reaction time?
I spent a week taking it to see if it had any effect on my vision. No controls. No scientific rigor. Let's just see what happens.
Originally posted on my personal website on 05-04-2021.
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Lutein and zeaxanthin are two carotenoids responsible for red and orange colors in nature. It’s also found in our eyes as a part of our visual processing system. I came across a paper claiming that raising lutein and zeaxanthin levels could improve reaction speeds. This paper found that even young people who supplemented the compounds found a benefit in speed. There are a number of conflicts listed in the paper too, so there are reasons to be skeptical – but whatever:
Funding: This study was funded by ZeaVision, LLC.
Two thoughts here:
I think it’s probably right to be suspicious of most of this stuff since there’s so much grifting around supplements.
It’s probably true that uncommon compounds in food can and do have some effect on your body in a way that isn’t well studied or understood. I used to think this was improbable because people have been eating these foods forever, but they really haven’t in these quantities.
So, if this is real, it’s interesting that you can just boost your reaction speed. It’s a key part of life: games, sports, driving, cooking. It’s also a pretty low risk thing to supplement. It looks like the biggest risk is that you could turn slightly orange from taking too much of it.
Let’s give it a try.
Our Test
We did one week of reaction speed tests without supplementation, and the second week with supplementation. This is way shorter than the four month test in the paper, but serum levels can peak after 16 hours and changes in macular pigment density can be seen within 7 days. Very few papers test for just a week though, so there’s also a chance that my 7 days of supplementation simply aren’t enough time to prove anything. Many of these papers say that changes take 8+ weeks to materialize, but I assume that if there’s improved macular pigment density within the first week, that there should also be some improvement to vision-related tasks even if the eye hasn’t been changed structurally yet.
Here’s what I did:
This was done with 15 reaction speed trials per day for a total of 7 days using Human Benchmark’s reaction test.
We always did this on the same device (a Macbook Pro trackpad) and shortly after coffee on an empty stomach.
Only difference was on the second week, where I took 50mg of lutein and 10mg of zeaxanthin with my coffee.
Week 1
We ended the week with an average reaction speed of 253ms across a total of 105 trials. An interesting detail is that we didn’t really improve during this week. There’s always a chance the improved speeds could come from practice, but on our last day we actually did slightly worse than our first day.
Also, I actually accidentally ate on Day 4 of the baseline trials (I don’t claim to have any rigor here). I had some eggs (which have lutein and zeaxanthin). Could that account for the best reaction speed of 235? Another interesting detail is Day 5 with the slowest score of 281. I had a beer the prior night and it appears to have a terrible effect on my score the next morning. Actually I was getting better until I did this…
Week 2
In the second week we did the same thing as the first, but supplemented with 50mg of lutein and 10mg of zeaxanthin early in the morning.
Again, this test was way shorter than the one in the paper but the results are pretty obviously better. Our new average was 226ms, nearly 30ms faster than the first week. Unlike the first week our times also improved daily, though we have no idea if that’s because of the alcohol, the practice, or the supplementation.
Results
There’s a pretty clear gap between the two weeks. It’s a sample size of 1, and I had a bunch of alcohol and eggs which definitely distorted the experiment. Also, I ran the experiment far shorter than any papers do, also distorting the experiment. But the data is interesting to me anyways:
Week 1 was clearly trending down until I had alcohol. Are we willing to believe that it wrecked my reaction time for 3 days? That seems plausible.
Week 2 starts really strong, below even the best day of Week 1. That’s pretty interesting, but it could be the cumulative effect of practice.
The end of Week 2 is the best, which you’d expect as either the result of practice or the supplements. It’s a bit weird that we go straight from 251ms at the end of Week 1 to 231ms at the start of Week 2 though. I’d expect if alcohol impacted my reaction speed, it should have also impacted my practice. This looks much closer to my result on the day I had eggs.
So: it’s inconclusive. The alcohol result is probably the most interesting detail. If the gap up in speed was as dramatic as alcohol’s, that’d be a much more interesting result. It’s entirely possible that you need to take this for a few months and allow for structural changes in the eye, but I don’t have any particular reason to right now.
The idea that you can just boost traits with supplementation is interesting though. I wonder how many other traits could be boosted from diet or supplementation alone. I suspect the answer is many.