Vitamin D is, without a doubt, the most incredible "vitamin"/prohormone/neurosteroid I have ever encountered. Frankly, I don't know how we got anything accomplished in health pre-D.
Unfortunately, people I meet rarely take their vitamin D in a way that accomplishes full restoration of vitamin D blood levels. It really isn't that tough.
Here's a list of common tripping points with vitamin D:
"I take vitamin D: 1000 units a day."
This is probably the most common mistake I see: Taking a dose that is unlikely to yield a desirable blood level. (We use 60-70 ng/ml of 25-hydroxy vitamin D as our target.) Most men and women require 6000 units per day to achieve this level. There is substantial individual variation, however, with an occasional person needing much more, a rare person requiring as little as 1000 units.
"I bought some vitamin D on sale. They were white tablets."
Time and again, patients in my office who initially have had successful vitamin D replacement, despite being reminded that only oil-based forms should be taken, switch to tablets. While they initially showed a 25-hydroxy vitamin D blood level, for instance, of 67 ng/ml on 8000 units per day with an oil-based capsule, they switch to a tablet form and the next blood level is 25 ng/ml. In other words, tablets are very poorly or erratically absorbed.
I have had people use tablets successfully, however, by taking their vitamin D tablets with a teaspoon of oil, e.g., olive oil. Oil is necessary for full absorption.
"I'm going to Florida. I'll stop my vitamin D because I'm going to lay in the sun."
Wrong. 90% of adults over 40 years old have lost the majority of their ability to activate vitamin D in the skin. A typical response might be an increase in blood level from 25 to 35 ng/ml--a 10 ng increase with a dark brown tan.
There is an occasional person who, with sun exposure, increases blood levels substantially. This can occur in both fair-skinned and dark-skinned people, though I've never seen it happen in an African-American person. The occasional person who maintains the ability to convert vitamin D with sun exposure, or young people, should seasonally adjust their vitamin D dose, e.g., 6000 units winter, 3000 units summer, or some other regimen that maintains desirable blood levels. You can see that monitoring blood levels (we check levels every 6 months for the first 2 years) is crucial: You cannot know what your vitamin D needs are unless you assess 25-hydroxy vitamin D levels.
"I drink plenty of milk. I don't think I need to take vitamin D."
Oh, boy. This is so wrong on so many levels.
First of all, no adult should be drinking plenty of cow's milk. (A discussion for another day.) Second of all, cow's milk averages 70 units of vitamin D, often the D2 form (ergocalciferol), per 8 oz. Even if the FDA-mandated 100 units per day were present, an average adult dose of 6000 units would require 60 glasses of milk per day . Can you say "diarrhea"?
Likewise, other food sources of vitamin D, such as fish (300-400 units per serving) and egg yolks (20 units per yolk), are inadequate. This makes sense: Humans are not meant to obtain vitamin D from food, but from sun exposure over a large body surface area. And this is a phenomenon that is meant to occur only in the youthful, ensuring that nature takes its course and us older folks get old and make way for the young (i.e., unless we intervene by taking vitamin D supplements).
"My doctor said that my vitamin D blood level was fine. It was 32 ng/ml."
Let's face it: By necessity, your overworked primary care physician, who manages gout, hip arthritis, migraine headaches, stomach aches, prostate enlargement, H1N1, depression, etc., is an amateur at nearly everything, expert in nothing. Nobody can do it all and get it right. Likewise vitamin D. The uncertain primary care physician will simply follow the dictates of the laboratory form that specifies "30-100 ng/ml" as the "normal" or "reference range." Unfortunately, the laboratory often quotes population distributions of a lab measure, not an ideal or desirable level.
To illustrate the folly of population distributions of a measure, imagine you and I want to know what women weigh. We go to a local mall and weigh several thousand women. We tally up the results and find that women weigh 172 lbs +/- 25 lbs (the mean +/- 2 standard deviations). (That's true, by the way.) Is that desirable ? Of course it isn't. Population average or population distribution does not necessarily mean ideal or desirable.
"My husband's doctor said he should take 4000 units per day. So I just take the same dose."
That would be fine if all adults required the same dose. However, individual needs can vary enormously. A dose that is grossly insufficient for one person may be excessive for another. Once again, vitamin D dose needs can be individualized by assessing 25-hydroxy vitamin levels in the blood.
"I don't need to take vitamin D. I already take fish oil."
I suspect this mistaken belief occurs either because people confuse fish oil with cod liver oil, which does contain some vitamin D. (Cod liver oil is not the best source of vitamin D, mostly because of the vitamin A content; also a discussion for another time), or because they've heard that eating fish provides vitamin D. However, fish oil capsules do not contain vitamin D unless it is added, in which case it should be prominently and explicitly stated on the label.
"I don't have to take vitamin D. It's summer."
For most people I know, if it's a bright, sunny July day, where are they likely to be? In an office, store, or home--NOT lying in the sun with a large body surface area exposed. Also, most people expose no more than 5-10% of surface area in public. I doubt you cut the grass in a bathing suit. Because of modern indoor lifestyles and fashion, the majority of adults need vitamin D supplementation year-round.
I advise everyone that gelcap vitamin D is preferable. Some, though not all, liquid drop forms have also worked. Take a dose that yields desirable blood levels. And blood levels of 25-hydroxy vitamin D are ideally checked every 6 months: in summer and in winter to provide feedback on how much sun activation of D you obtain.
If your doctor is unwilling or unable to perform vitamin D testing, fingerstick vitamin D test kits can be obtained from Track Your Plaque.