Vitamin D is good for more than preventing Rickets. It helps at this time of year for depression and immune function. When physicians talk about vitamin D deficiency, they are invariably talking about low levels of an inactive compound called hydroxyvitamin D 25 or "25 (OH) Vitamin D3" as doctors write it. But there's another 1,25 form which is biologically active.
Our kidney has the lovely task of converting D from inactive 25 form, to the active 1,25 form, and magnesium is necessary for that conversion. Kidney compromise means suppressed D activity and reduced 1,25 levels. As much as I love vitamin D, toxicity can occur if you take too much D which triggers low magnesium and high calcium. The picture of this includes heart palpitations, nausea, constipation, kidney stones, memory loss, softening of bones, hyperparathyroidism and body aches.
Today I'll teach you about vitamin D testing. Most physicians measure your blood levels of vitamin D 25 (the inactive form). This type of D grabs hold of your vitamin D receptor (VDR) and renders it inactive. Darn! Now the cell can't grab on to the 1,25 form of D which is what you want! I don't advise you supplement based upon low 25 D levels (seen on lab tests) because that is only half the picture. Take one blood test but ask your doctor to evaluate two biomarkers:
1,25 (OH) Vitamin D3: Active
25 (OH) Vitamin D3: Inactive
This ratio should be less than 2 to 1. Ratios above 2 to 1 may be associated with infectious pathogens and high pro-inflammatory cytokines. You would think a high amount of the 1,25 form is desirable but it's not. It could spell parathyroid disease, sarcoidosis, rheumatoid, fibromyalgia, Lyme and many other infections. On the other hand, low levels of 1,25 (active) D can occur with kidney disease since the kidneys are unable to activate the 25 form to 1,25. Hitting the nail on the head is important to your health.
Example: Your lab reveals a level of "1,25 D" of 60, and a "25 D" level of 20. Hopefully, the units are the same. The ratio of 60 to 20 equals 3. Since the ratio of 3 to 1 is greater than 2 to 1, you don't need to supplement.
If your ratio was 2 to 1 (or less) that's great. It might be okay to supplement but only to a point, because you don't want the total 1,25 D to get above 75 (considered the upper range by many health experts).
Personally, I wouldn't supplement based solely upon low levels of the 25 D. It's inactive. It's what you see on your labs. The reason is because your active 1,25 levels might be fine, or even high. And just because you supplement doesn't necessarily mean you activate that D either! I think you should get the full picture and evaluate both forms of D. It's scary that over 100 drugs impact your D and calcium levels. All that information is in my Drug Muggers book.