I was going to make this post something completely different, but then I got my annual physical results back. Everything was normal except one thing: my vitamin D levels. Admittedly, I am a little embarrassed about it. After all, I’m a dietitian. This should be my forté. But the truth is I am just as surprised as you are.
I begun supplementing 1000 IU of vitamin D again before the new year, fresh off a sun-filled trip to Sydney. I knew I wouldn’t be getting enough sun over winter so I turned to capsules for my daily D fix.
What makes my physical results even more interesting is that I take greater than the recommended amount of vitamin D. The Institute of Medicine recommends 600 IU a day, and I’ve been taking 1000 IU. Sure, my vitamin D levels weren’t low enough for my doctor to recommend a super dose, but I still fell short of the optimal range.
Like any good dietitian, I went searching for explanations. This is what I found:
#1: It could be in my DNA.
There are several genetic variants that affect vitamin D status. I might have one or more of those variants, which means that I naturally need more vitamin D than the average Jo.
#2: Weather REALLY matters.
Vitamin D production from cholesterol and UVB rays is the biggest source of vitamin D for most. When sun exposure dips, so does vitamin D synthesis. This winter has been particularly cold and wet in San Francisco, which means that I have probably seen less UVB rays than usual.
#3: I eat very little vitamin D.
Unlike other vitamins, it’s really hard to get adequate vitamin D through food. Vitamin D is only found in a handful of foods, and not all of them are delicious (at least in my book). Milk is fortified with vitamin D, and fatty fish like sockeye salmon contains some too. Other foods rich in vitamin D include: cod liver oil, swordfish and tuna, but you need to be eating those daily to meet the recommendations.
#4: Dodgy D supplement? Maybe.
In the US, supplement testing is the responsibility of the manufacturer, which means quality varies wildly between brands. I’ve been taking an off-the-shelf supplement that claims to provide 1000 IU per capsule. Perhaps my vitamin D supplements offers less than listed on the label?!
What Am I Doing Now?
The end result of all of this is that I have doubled my daily vitamin D dose from 1000 IU to 2000 IU. As the weather warms-up, I will probably drop my dose back down to 1000 IU, switch to one of the brands independently tested by Labdoor, and ask to be retested. Perhaps I won’t need to supplement at all during the summer months. We'll see.
Why Vitamin D Status Matters
I will keep it brief but Vitamin D has long been touted as a bone-builder. In addition, recent studies have shown that vitamin D is also involved in:
Maintaining the immune system and possibly protecting against some autoimmune diseases ;
Mitigating heart disease and cancer risk [2,3] and;
Protecting against cognitive disorders such as Alzheimer’s disease .
Vitamin D status matters. A lot. If you haven’t gotten your levels checked recently, do it. If I was low on vitamin D and supplementing, you might be low too, and that comes with risks.
 Vitamin D. Linus Pauling Institute Micronutrient Information Center. Updated 2014. Accessed on December 30, 2016.
 Does sufficient evidence exist to support a causal association between vitamin D status and cardiovascular disease risk? An assessment using Hill's criteria for causality. Weyland PG, Grant WB, Howie-Esquivel J. Nutrients. 2014 Sep 2;6(9):3403-30. doi: 10.3390/nu6093403. Review.
 Vitamin D and Colorectal, Breast, and Prostate Cancers: A Review of the Epidemiological Evidence. Jacobs ET, Kohler LN, Kunihiro AG, Jurutka PW. J Cancer. 2016 Jan 5;7(3):232-40. doi: 10.7150/jca.13403. Review.
 Vitamin D in dementia prevention. Annweiler C. Ann N Y Acad Sci. 2016 Mar;1367(1):57-63. doi: 10.1111/nyas.13058.