Vitamin D Overdose: Can You Take Too Much?
- Thursday, 24 November 2011
Interest in vitamin D is at an all time high and there’s no sign of it letting up with more and more clinical trials being conducted and more on the way. With increased interest comes increased enthusiasm and more and more people are starting to take vitamin D supplements, which vitamin D experts not only think is a good idea but advocate.
Vitamin D deficiency, as defined by the vitamin D pioneers, is a blood level below 30ng/L or 75nmol (although this cut off is edging up to 40ng/l or 100nmol). Deficiency is the norm in North America and not the exception, given that for many months of the year, there isn’t sufficient UVB from sunlight to produce enough . Even for those living in the southern US where there is sufficient UVB, most people spent a lot of time indoors and are not spared the risk for deficiency. Given this, supplementation with vitamin D is paramount but can you take too much?
In a word. Yes. But then again, anything can be toxic if too much is taken. The best example is water, if you drink too much in a short period of time, your sodium levels can be diluted and you’ll have seizures, remember the expression: the dose makes the medicine or the poison.
In a perfect world, you would test your vitamin D and depending on the level, take an appropriate amount for about 3 months and then retest to see if you’ve reached your target blood level. The lower your blood level of vitamin D at the outset, the greater the response will be to supplementation. As blood levels rise, so does the response to the same dose of vitamin D.
Starting blood level of vitamin D
Vitamin D dose
Increase in vitamin D blood level
10ng/L or 25nmol
11ng/L or 27.5nmol
30ng/L or 75nmol
8ng/L or 20nmol
50ng/L or 125nmol
5ng/L or 12.5nmol
90ng/L or 225nmol
1.6ng/L or 4nmol
If you’re not inclined to have your vitamin D levels checked, you can confidently ensure you’re getting the Upper Limit or UL of 4000IU per day from all sources (food, sunlight and supplements) set by the Institute of Medicine. At this level, 98% of the population will achieve 48ng/L or 120nmol. Some people will need more vitamin D to achieve this level and some will have blood levels slightly higher than 48ng/L or 120nmol but not by much. Referring to the chart above, toxicity would not be expected even if they managed to get some judicious sun exposure.
It is estimated that, on average, diet contributes about 200IU per day, under the best conditions, 2000IU from sunlight (but this is highly unusual since most don’t have access to adequate amounts of UVB year round and for those would do, most spend their days in doors, so the taking up to 4000IU, or the total UL, from supplements is perfectly safe the experts says. This is especially true given that the No Observed Adverse Effect Level or NOAEL is 10,000IU per day, an amount where there’s never been a recorded case of toxicity. The UL of 4000IU takes into account a large safety margin of 6000IU compared to the NOAEL.
So to take advantage of the many health promoting benefits of vitamin D, go forth, and supplement but do so prudently and don’t forget to ensure you are getting enough of vitamin D’s supporting nutrients.
To convert from ng/L to nmol/L
To convert from nmol/L to ng/L