As time passes, I gain greater and greater respect for the power of restoring vitamin D blood levels to normal, i.e. 50-70 ng/ml. Just yesterday, I saw several people with blood levels of <10 ng/ml--severe deficiency.
Vitamin D deficiency this severe poses long-term risk for osteoporosis, arthritis, colon cancer, prostate cancer, inflammatory diseases, diabetes, and heart disease. Vitamin D appears to make coronary plaque reversal--reduction of your heart scan score--easier and faster.
But it is important that you take the right kind of vitamin D. Several of the people I saw yesterday with vitamin D levels of somebody living in total darkness were taking vitamin D, but they were taking tablets . Tablets are the wrong form. Powder-based tablets, in my experience, yield little or no rise in blood levels. Some preparations generate a small rise but the dose required is huge.
If you're going to take vitamin D, take a preparation that yields genuine and substantial rises in blood levels. This requires an oil-based capsule. I commonly see blood levels of 25-OH-vitamin D3 rise from, say, 10 ng/dl to 60 ng/ml when oil-based capsules are taken.
The most common dose I prescribe to patients is 2000 units per day to females, 3000-4000 units per day to males in non-sun exposed months. Ideally, your dose is adjusted to blood levels.
The Vitamin Shoppe preparation pictured here is one I've used successfully and generates bona fide rises in blood levels. And it costs around $5. Just be sure the preparation you buy is oil-based.