Vitamin D – Sources & Amounts

Technology is great.  A couple taps on my phone lets me confirm medical appointments, check test results, or even communicate with my doctor.  It seems incredibly efficient for my doctor to be able to make notes when reviewing lab results and not have to task someone to make phone calls.  Just like that, I saw the note:

RECOMMEND ADDING EXTRA 1000 IU OF VITAMIN D TO DAILY REGIMEN

Since I could see the lab’s numbers, that recommendation wasn’t really a surprise.  Vitamin D might be easy to get in the tropics, but deficiency is pretty common in the rainy Pacific Northwest since the best way to get Vitamin D is from sun exposure and we don’t have a lot of sunshine.  So how do we get Vitamin D?  And how much do we need?

Vitamin D is primarily synthesized in our bodies based on exposure to sunlight. Think of it like photosynthesis for people (thankfully we don’t turn green!). Both the liver and the kidneys play a part. But if we’re missing the initial sunshine step, it’s pretty difficult for the kidneys and liver to do their part. Although it’s theoretically possible to get Vitamin D through our diet (our liver & kidneys do the same hydroxylations whether our Vitamin D is acquired through diet or sunshine), there aren’t that many dietary sources.  Foods containing vitamin D include fish, eggs, UV mushrooms, and pork. That’s a pretty short list.  I’m not counting fortified products, since the whole point is to find nutrient-dense foods instead of taking supplements.  Hiding supplements in the food doesn’t change the fact that they’re supplements instead of naturally-occurring.  Plus the fact that the foods they add Vitamin D to are mainly dairy products, ensuring that people who don’t get calcium from dairy also don’t get Vitamin D.  But if you consume dairy products, you can add that as a Vitamin D source, too.

So What Does Vitamin D Do for Us?

Vitamin D does more than just prevent rickets in growing kids. It reduces inflammation (!), modulates cell growth, helps us metabolize glucose, affects immune function, and helps build strong teeth. 

A major job of Vitamin D is to help us absorb calcium.  We can take all the calcium pills we want, but if we’re not getting enough Vitamin D, the calcium is not going to do much good – and our meds can affect things further. For instance, prednisone interferes with Vitamin D. Everyone taking DMARDs is at increased risk for osteoporosis, so metabolizing calcium is extremely important, which means that Vitamin D is important.  People taking Disease Modifying Anti-Rheumatic Drugs need to be particularly careful to get enough Vitamin D so that their calcium is properly absorbed or they could end up with soft bones.  Who needs more problems?

But there’s more.  There is a clear link between MS and low 25(OH)D levels. Will future studies show a link to other conditions?  Studies are still underway because data from previous studies is unclear. There could be a link between low Vitamin D and cardiovascular disease (which is already a risk for people with autoimmune diseases).  The data on the link between Vitamin D and cancer is conflicted, but it appears that both too little and too much might increase the risk of cancer, and that Goldilocks-right-in-the-middle amounts might decrease mortality in people who get cancer despite having good Vitamin D levels. There are also studies on a link between low Vitamin D and type 2 diabetes.  Another study seems to indicate that overweight people can increase their Vitamin D levels by losing weight, the thinking being along the lines of D getting trapped in the outer fat cells – losing that fat then makes the D available to metabolize.  It’s fascinating.

Do We Really Need 15 mcg Per Day?

There is a tidy little chart listing US Recommended Dietary Allowances that says everyone should consume 15 mcg a day until age 70, when it goes up to 20 mcg.  But then there’s the fine print.  That’s dietary Vitamin D assuming minimal sun exposure. Those getting plenty of sunshine on their skin wouldn’t need as much Vitamin D from their food. 

On the other hand, not everyone agrees with the US RDAs.  Only 10 mcg are recommended in the UK.

Labs Can Measure Blood Serum Vitamin D

The amount of dietary Vitamin D we take in doesn’t correspond directly to the amount in our bloodstream.  Doctors can order a lab test to check our levels. The reliability of that test is questionable, but we work with what we have and use the Food & Nutrition Board’s definitions of appropriate levels of Vitamin D. I note that the lab I use has slightly different definitions:

Before we get too dogmatic about those number being etched in stone, we need to recognize that the NIH fact sheet on Vitamin D tells us,

“Optimal serum concentrations of 25(OH)D for bone and general health have not been established because they are likely to vary by stage of life, by race and ethnicity, and with each physiological measure used. In addition, although 25(OH)D levels rise in response to increased vitamin D intake, the relationship is nonlinear. The amount of increase varies, for example, by baseline serum levels and duration of supplementation.”

Basically they’re saying that nobody knows for sure how much Vitamin D we truly need, but they’ve taken as good a guess as they can.

Then there’s the Endocrine Society, which says that people should get as much Vitamin D as it takes to keep their serum 25(OH)D levels above 75 nmol/L (30 ng/mL).  That’s quite a bit higher than the Food & Nutrition Board’s recommendation that 50 is adequate.

Putting everyone’s guesses together, I take it to mean that ideal serum levels would be in the 75-96 range, and we need to figure out a safe way to get our Vitamin D to that level.

But we have to be careful. As with other fat-soluble vitamins, toxicity is a real possibility. Current theory tells us that 1,000 IU daily can raise the serum level by 10 ng/mL, so that much supplementation should theoretically be safe for people whose numbers are low.  The Tolerable Upper Limit for adults is 4,000 IU, so 1,000 should be perfectly safe.  Don’t take too much, though.  Toxicity sounds not just unpleasant, but dangerous: nausea, vomiting, pain, dehydration, kidney stones, renal failure, heart problems, or death.

Note that those scary results of toxicity are thought to be from supplements. Getting Vitamin D from sunshine and food is considered safe.

Which foods contain Vitamin D?

Six ounces of salmon or swordfish contain 142% of the daily Vitamin D we need.  An equal amount of halibut provides 50% of our day’s Vitamin D.  A three-ounce can of tuna provides 9%. 

Supposedly a 1-cup serving of crimini mushrooms has zero vitamin D, unless they’ve been treated with UV light, in which case they provide 122% of our daily Vitamin D.  This is most peculiar. I’m not sure if it means we should be setting our mushrooms out in the sunshine before consuming them, or what the deal is, but if I had sunshine, I could set myself in it instead of my mushrooms. 

Basically, unless you’re eating a ton of salmon every day or drinking milk, it’s nearly possible to get enough Vitamin D without taking supplements or going out in the sun.

How Much Sunshine Do We Need?

We don’t need as much sunlight as you might think. Up to one hour three times a week should be sufficient. Note that since Vitamin D is fat soluble, extra is stored (as opposed to water-soluble vitamins that are excreted if we get more than we need).  It appears that we can spend time in the sun every-other-day, not daily.

How long we should spend in the sun depends both on how dark our skin is and on how intense the sunlight is.  We just need to know the UV index – and I’ve discovered that my smart watch can provide that information. It’s also possible to check the weather forecast for the UV Index.

It’s not enough to look out the window to see if it’s sunny or not. UV index depends on other factors, including angle of the sun (ie time of day and season of the year). For instance, it’s a beautiful day here, but the sun is so low that despite the blue sky, the UV index is only 2.

Once I know the current UV index, GB Healthwatch has a handy table for looking up how much time is needed in the sun (while wearing shorts and a t-shirt). Unfortunately, they don’t document where the data came from. Nonetheless, it’s a starting point.

Conclusion

The average person needs 15 mcg of dietary Vitamin D, every day, or needs to spend up to an hour getting sunlight directly on the skin (directly, not through a window). The farther from the equator people live, the less likely they are to get adequate Vitamin D from the sun, so supplements might be needed. It’s also possible (but fairly expensive) to use a special UVB light or spend time in a tanning bed.

People with autoimmune diseases need to be especially vigilant in getting enough Vitamin D, both to help control inflammation, and to reduce the probabilities of complications such as cardiovascular disease and osteoporosis.

Wishing you well!

***** ****** ******

1 Food & Nutrition Board
2 National Academies of Sciences, Engineering, and Medicine

Resources:

*Vitamin D Fact Sheet for Health Professionals

*Vitamin D: A Rapid Review

*Get Vitamin D from Sun Exposure

*Top Ten Vitamin D Foods

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