Typically, Vitamin D is measured by levels of 25(oh)D3. The units are usually Ng/ml but can be
Nmol/L. Optimal is 50-70Ng/ml or 125-175Nmol/L. Average, upon which normal lab values are
based, is 30-100. I would aim for optimal, not average.
Additionally, be aware of risk factors for osteopenia (mild weakening of bones): foods and chemicals that acidify the body elicit a neutralizing of acid in blood by drawing calcium carbonate out of bones because it is alkaline. At the top of this list are sodas and other soft drinks containing phosphoric acid, and coffee. Next are animal products containing protein and fat, made of amino and fatty acids respectively. Moderately acidifying foods include vegetable proteins. Grains are mildly acidifying.
Alkalizing foods (which neutralize acid and protect bones) include fruits and vegetables, including foods that go in acidic but have an alkalizing affect on the body, such as citrus and apple cider vinegar and seaweeds (though one might be careful of where the seaweed comes from as they pick up toxic metals as well as beneficial minerals). Acid can also be neutralized by tablets of calcium carbonate, sodium bicarbonate (baking soda) and egg shells (ground up and put into the coffee maker along with the coffee grounds).
Of note, scientists can not grow cancer cells in a neutral or alkaline environment. Many think there are many benefits to balancing pH. Many foods believed to be protective against cancer are alkalizing. Optimal Vitamin D levels are also protective of many organs and systems of our bodies.