My vitamin d level was 21 (normal is 32-100). my doc recommend 2,000 iu daily. is that enough to bring it up?

Vit D: it should be enough. some sun exposure will be good. make sure you protect yourself with sunscreen. usually 10-20 min a day is good enough. take mild and milk products. some of them are fortified with Vit D. Follow up with doctor as excess of Vit d supplementation can cause toxicity.

Why take it?: What's the reason your doctor is trying to treat that level of vitamin D? There isn't much data showing any benefit for increasing vitamin D levels which are in the 20's. Perhaps if in the 10's then it would make sense but otherwise I would respectfully question your need for supplementation. To answer the question, that's probably too low to raise your vit D level.

Yes: No reason to be more aggressive than that. 2000 is a perfectly reasonable starting dose. If after a few months it still isn't in the normal range you can always increase it, but there is a mantra in medicine: "start low and go slow." In other words, use the lowest effective dose.