Check out the Peripheral Neuropathy forum--a lady who was low in Vitamin D3 asked for some help in deciding how much she needed to take and MrsD responded.

She told her that the general rule for D3 supplements is 1000IU D3 daily for every 10 points you need to raise. So use a level of 50 as your goal. At 38, you may only need 1000 IU D3 daily.