HOW MUCH VITAMIN D?
You’ve seen the blogs and headlines. It seems like everyone is warning us about the dangers of vitamin D deficiency. And some experts make it sound like it’s almost impossible to get too much vitamin D.
I have tried to report to you some of the excitement and controversy in the vitamin D field in my previous “Tips From the Professor”
Just to review: In 2010, the Food & Nutrition Board of the Institute of Medicine set the RDA for vitamin D as 600 IU between the ages of 1 and 70 and 800 IU over 70. The Food and Nutrition Board set 4,000 IU/day as the Tolerable Upper Intake Limit. In plain English, that means that daily intakes above 4,000 IU/day have the potential to be toxic in some individuals.
I pointed out to you that the RDAs were based primarily on the amount of vitamin D needed for healthy bones. While there is emerging evidence that higher intakes of vitamin D may be helpful for a strong immune system and for reducing the risk of heart disease, cancer, diabetes and autoimmune diseases, the Food and Nutrition Board did not consider those data to be definitive enough to serve as a basis for RDA recommendations.
I also alerted you to fact that blood levels of 25- hydroxy vitamin D were a better indicator of vitamin D status than the amount of vitamin D in the diet (more about that latter). The Food and Nutrition Board stated that blood levels of < 30 nmoles/L of 25-hydroxy vitamin D indicated a severe deficiency likely to lead to rickets in children and osteomalacia in adults; 30-50 nmoles/L should be considered as a deficiency that could affect bone and general health of the individual; levels above 50 nmoles/L should be considered as optimal; and levels above 125 nmoles/L had the potential to be toxic.
I have also shared my personal recommendations with you in previous "Tips". I personally consider the data on the health benefits of vitamin D to be strong enough for most people to want to aim for an intake of 1,000 to 2,000 IU/day of vitamin D.
And, because the relationship between vitamin D intake and blood levels of D vary tremendously from individual to individual, I have also strongly recommended that everyone get their blood levels of 25-hydroxy vitamin D tested and let their doctors use those levels to determine what their daily intake of vitamin D should be.
Finally, I have recommended that people not exceed 4,000 to 5,000 IU/day of vitamin D unless directed to do so by their doctor.
But what about those "experts" and blogs that recommend intakes of 5,000 - 10,000 IU/day and blood levels of 25-hydroxy vitamin D exceeding 75 nmoles/L? Do they know something that the rest of us don't?
With that question in mind, I want to share with you two studies that have just been published in The Journal of Clinical Endocrinology & Metabolism.
The first study (Durup et al., JCEM, doi:10.1210/jc. 2012-1176) looked at blood levels of 25-hydroxy vitamin D in 247,574 private practice patients in Copenhagen and recorded how many of them died over the next 3 years. (The Danes archive all patient data in a centralized database making these kinds of large scale studies possible).
What they found was not too surprising. They reported that the lowest death rates occurred in patients with blood levels of 50-60 nmoles/L of 25-hydroxyvitamin D. (They cited previous studies showing the lowest death rates in patients with serum 25-hydroxy vitamin D in the 50-80 nmoles/L range - which was fully consistent with their data).
They also found, in agreement with previous studies, that serum vitamin D levels both below and above the optimal range were associated with a significant increase in mortality.
At the lowest blood levels (10 nmoles/L) the risk of death was 2.3 times greater, and at the highest blood levels (140 nmole/L) the risk of death was 1.4 times greater than for those patients in the 50-60 nmoles/L range.
The authors of this study estimated that an intake of 5,000 IU/day for an extended period of time might be sufficient for someone to reach the 140 nmoles/L blood level of 25-hydroxy vitamin D. But this is where the second paper is of interest.
This study (Autier et al., JCEM, doi: 10.1210/jc.2012- 1238) was a systematic review of 76 previous clinical studies comparing dietary intake of vitamin D with blood levels of 25-hydroxy vitamin D. They reported an average increase of 1.9 nmoles/L 25-hydroxy vitamin D for every 40 IU increment of vitamin D intake.
However, the really interesting observation was that the increase in 25-hydroxy vitamin D per IU taken in varied 3 to 4 fold from one study to the next! While some of that variation can be ascribed to differences in measurement methodologies, it also illustrates the difficulty in predicting blood levels of 25-hydroxy vitamin D based on vitamin D intake alone.
So what is the bottom line for you?
1) Aim for at least 600 IU/day of vitamin D (800 IU if you're over 70) from diet and supplementation if you want strong bones.
2) 1,000 to 2,000 IU/day is probably better if you're looking for some of the other health benefits of vitamin D.
3) Don't exceed 4,000 to 5,000 IU/day unless directed to do so by your health professional.
4) The level of 25-hydroxy vitamin D in your blood is the best measure of your vitamin D status and the best guide as to how much dietary vitamin D you should be getting on a daily basis.
5) Although I didn't talk about it in this article, sun exposure also counts - just don't overdo it.
To Your Health!
Dr. Stephen G Chaney
P.S. If you like more information about vitamin D from
a reliable third party source, I recommend you go HERE