My vitamin d- 25-oh was <12.8 when ref range 30-80. do i have a health problem or do i just need a supplement?

Not necessarily: Low Vit D levels increase risk of many serious health problems and can cause many different symptoms, but a young otherwise healthy person may have no significant health problems that have yet developed. Most adults need 5-8000 iu of D3/day to achieve optimal levels, though this time of year being in the mid-day sun can give your adequate D. See http://bit.ly/1eKkVkv &amp; http://bit.ly/1dC7vnA