Interesting. I wonder now then what I experienced was accidental. For about 2 months, I was on a yam-heavy safe starch diet. I consumed probably 400g+ of orange yams daily during that span (about 3 medium-sized orange American Southern yams).
I noticed my vision becoming very cloudy and blurry at night. I also occasionally (once or twice a week) take 2 tsps os Carlson's Cold Liver Oil, which has 850 IU of Vitamin A per teaspoon. When I did, I noticed my vision clearing up almost immediately. I also noted my sudden craving for the CLO (LOL) like an iron-deficient person craving ice.
Could this be that the excessive consumption of orange yams had anti-Vitamin A properties, resulting in paradoxical Vit A deficiency? The result is paradoxical, just like the linked article points out, because the beta carotene doesn't always convert to Vit A as assumed but blocks Vit A.
(But then do we really have to wonder? Taking calcium actually increases cardiovascular risk. Taking resveratrol in supplement form doesn't seem to lengthen longevity. Large intakes of fish oil could increase the risk of cancer.)
But the crux here is that this occurred when I was eating yams high in beta carotene, not any supplements. If so, this is very alarming indeed! In the above cases where vitamins had unintended effects, they were in the form of isolated nutrients.
Anyone on a high safe starch, orange yam diet experience vision anomalies like I did? If so, then, try taking some cod liver oil and see if the anomaly clears up. My tale seems to confirm the article's findings. And Indeed, the beta carotene anti-Vit carotene's anti-Vitamin A effect doesn't seem to be just limited to supplements. Confusing, huh? Before, we thought Beta Carotene was good for vision; now we're told, only up to a certain amount. But how do you know you've reached the tipping point? I was only trying to replicate the Kitavan diet in my experiment.