If you are concerned about vitamin D levels please have them checked--if possible, by an endocrinologist or someone who can get you to one as soon as your levels are low. Too low can be critical. And menopause is NOT the primary sign for checking for parathyroid levels or osteopoenia.
I do not make vitamin D hardly at all. I have to be on extremely high supplemented levels under doctor supervision (100,000 iu's a week).
I had hyperparathyroid and osteopoenia at 37
I have not gone through menopause.
There is also a difference between D2 and D3 but I can't find a lot about it.