I assume you were talking about Vitamin D, since quercetin is not a nutrient. The Endocrine Society recommends a blood level of 40-50 ng/ml as optimal, and there are several journal papers that show there is a health benefit from 70 ng/ml for MS patients (like me). There is even a report of a group that is giving MS patients a whole lot more, like to get a blood level of 250 ng/ml. Their MS symptoms disappeared.

But that truly IS a mega-dose. They have to highly restrict their calcium intake to avoid calcification in their organs. 70 ng/ml is the blood level they measure in lifeguards in Hawaii. That's where the body stops absorbing sunlight to make Vitamin D, and nobody thinks you can overdose on D from sun exposure.

So no, I would never advocate anybody take an overdose of a fat soluble vitamin. People can die from that.