This is a great point. Vitamin D deficiency causes problems, and should be treated. 5000 units a day can be great for treating a deficiency - until you are no longer deficient. The answer for you is checking your Vitamin D 25-OH level. If it is still low (under around 30), then you may need the high dose. If it is getting too high (above 60) then you need to back off. There isn't a one-size-fits-all dose for everyone.