What's a recommended daily dosage of otc vitamin d supplement? should it be taken with food?

It depends...: Dose is individualized, but most adults need 5000-8000 iu/day in fall & winter for optimal levels. You can get toxic from too much but doses below 40, 000 iu/day are safe. If you spend time in the mid-day sun in spring & summer without sunscreen don't need to take in those months.Check levels. See http://articles.Mercola.Com/sites/articles/archive/2011/11/30/taking-the-right-type-of-vitamin-d.Aspx.

Find blood levels: Many people are vitamin d3 deficient, and it's important to have enough. So you're right to pursue this. A blood test to know your level is the best thing to get. That way you can supplement with the right amount. Until you know that it's safe to take up to 5000 units per day.