- Most natural vitamin D comes from the reaction of the sun on our skin. If you stay indoors a lot - i.e. car to desk job to car to house - and/or wear sunscreen when outdoors, then you are probably not getting much Vitamin D from the sun.
- Vitamin D is found naturally in very few foods. The main source is the flesh of fatty fish like cooked salmon, tuna, and mackeral as well as fish liver oils (i.e. cod liver oil). If you don't eat fish very often. them you're likely not getting much naturally from your diet.
- Some foods are fortified with Vitamin D - mainly milk. Some yogurt and margarine is also fortified. If you don't drink much milk, you're likely not getting much from your diet. One cup of milk has abut 100 IU Vitamin D.
*note: I checked my fridge and cupboards.. I have only two things that can contain Vit D: 1) Clif Builder's Bar - 1 bar has .00068 mg which seems like very little; 2) PC blue menu Celeb non hydrogenated, calorie reduced margarine. 2 tsp has 30% of recommended daily intake. I eat 2 tsp only once per week probably. So clearly, I'm not getting much from my diet.
- Certain groups of individuals are predisposed to deficiency and therefore more likely to need supplementation. These include: the elderly and people with dark colored skin (their skin doesn't make usable vit D from the sun as readily); obese (subcutaneous fat holds onto vit D and doesn't release it as readily into the circulation); people who have had gastric bypass and those that have fat malabsorption conditions; and breast fed babies (especially if mom has low vitamin D and baby isn't exposed to much sunlight).
- Tanning beds do supply UV radiation that triggers skin to make vitamin D.. but tanning beds also predispose to skin cancer so regular use is not recommended.
- Exposure to sunlight through glass will not result in vitamin D synthesis so sitting in a sunny office or driving all day won't boost Vitamin D.
If you have decided you are not getting enough Vit D and want to supplement, remember that too much of a good thing can be dangerous, so DON'T OVERDO IT. As I say in The Rebel Diet, "the dose makes the poison and the dose makes the cure." Unlike the water soluble vitamins B and C, vit D is fat soluble so we won't simply urinate out the extra - we'll store it in our fat and this can lead to overdose.Vitamin D toxicity is associated with weight loss (hey..not bad), but also heart disease, increased rates of cancer and increased falls and fractures in the elderly.
So how much supplementation is recommended? The RDI (recommended daily intake) for Vitamin D for adults is 400-800 IU/day. If you haven't been getting much sun and don't eat many food sources of Vit D, then you can get this through a supplement. If you feel you have a deficient level because of a lack of sunlight and food sources, then supplement with 1000 IU - 4000 IU (maximum) for a few weeks to get your levels up to snuff, but then aim for 1000 IU daily; this should do the trick and keep you in a good range. *Of note, prolonged sun exposure wil not lead to vitamin D toxicity because our skin regulates it and won't overproduce the vitamin D.
Here's the recommended UPPER LIMIT intake for Vitamin D so do not go above this:
Me personally, I take 1-2 vitamin D drops (1000 - 2000 IU) per day in the winter months (when I remember). And I only remember sometimes. And I get at least 10 minutes per day outside with walking to and from the subway (although only my face is exposed and my moisturizer is SPF 15). Sigh.. Too bad my almond milk isn't fortified..
If you are going to get your blood level tested, ask your doc to test 25 (OH) D and aim for a level between 50 - 75 nmol/L. Even though blood test reference ranges say that 25-75 nmol/L is insufficient and that 75-250 is sufficient, studies have shown that having blood levels consistently above 75 nmol/L has been associated with increases in all cause mortality, pancreatic cancer and cardiovascular events.
My recommendation - 1000-2000 IU daily when you're getting very little sun will keep you in a good, safe range (it's difficult to get blood levels above 75 nmol/L at this dose) wherein you'll reap the health benefits but avoid the health risks.
