Image taken by Paige Kyle
It’s winter, it’s Michigan, and the weekly forcast is unchanging: Cloudy, chance of snow showers, high of 23 degrees. As the motivation to get outside steadily declines because of windchill factors and frostbite warnings, you might want to consider something else this season–are you getting enough vitamin D? If you live in Michigan during the months of November-March, the literature suggests probably not.
Vitamin D is known for its critical role in regulating calcium levels in the blood within a narrow range. If calcium levels decline due to inadequate intake, vitamin D can act as a hormone to signal the removal of calcium from the bone in order to maintain appropriate levels. Thus why vitamin D deficiency can lead to poor bone health and can result in a painful condition in adults known as osteomalacia. In children, this same condition is known as rickets. Symptoms can include numbness in the extremities, softening of the bone, higher risk of bone fractures, and overall bone pain. Once properly treated with a combination of vitamin D, calcium, and phosphorus, adults can expect to completely recover (2).
Deciding on the recommended levels of vitamin D for the US population has been a long running debate among the research community. Consequently, this has lead to some confusion among the general public about how much vitamin D is really necessary. In 2011, IOM released a new report that took several studies into account to determine the recommendations and upper levels (IU/day) for different age groups.
Here’s what they came up with:
Image taken from http://www.iom.edu/~/media/Files/Report%20Files/2010/Dietary-Reference-Intakes-for-Calcium-and-Vitamin-D/Vitamin%20D%20and%20Calcium%202010%20Report%20Brief.pdf
What is an upper level?
Think about the upper level as the maximum level at which a nutrient is beneficial to human health. The upper level for vitamin D for adults is 4,000 IU/day. But, don’t let this level scare you. Even if you are drinking 3 glasses of milk (100 IU/8oz) per day, taking a multivitamin (~400 IU) every morning, eating wild-caught salmon for dinner (~900 IU/3.5 oz) every night of the week, reaching 4,000 IU/day is difficult to do.
Other influences on vitamin D production:
AGE
It has been well defined that as we age, the ability to synthesize vitamin D from the sun starts to decline. When subjects were exposed to equal amounts of sunlight for 15 minutes, the older subjects (62-80 years old) had much lower maximum vitamin D concentrations than the younger subjects (1). As a result, the IOM increased the recommended daily dose of vitamin D for this age group (70+ years) from 600 to 800 IU/day.
ETHNICITY
Skin pigmentation is actually just the result of something called melanin that is present in the skin. To put it simply, those who have darker skin also have more melanin. It turns out that melanin acts similar to sunscreen and competes for the absorption of sunlight. In the process, there is less vitamin D synthesized in the skin. In a 2012 CDC report, researchers classified Non-Hispanic Blacks as a high risk group for developing vitamin D deficiency.
What does this mean for us this winter?
As a nutrition student, I hate to say it, but it looks like in the “supplement vs diet” war, the supplement wins this battle at least for 3-4 months out of the year. With that said, it should also be no surprise that the general population isn’t very good at taking a routine vitamin D supplement. According to the 2009-2010 National Health and Nutrition Examination Survey, it’s even more of a concern if we look at individuals between the ages of 20-39. Yes, my fellow peers, this means you. The older and the wise once again have us beat on this front. The survey showed a staggering 15% of US Males in this age group reported taking a vitamin D supplement; US females just coming out ahead at 18%. Also not surprisingly, national milk consumption statisitics didn’t fare well either for both adult age groups. From 2005-2006, average milk consumption for adults over the age of 20 was less than 3/4 cups of milk per day (less than 100 IU of vitamin D).
Recap: If you’re not making sufficient vitamin D from the sun during the winter, you’re not fitting in those 2 glasses of fortified milk per day, and you’re not taking a multivitamin every morning, then how are you reaching the recommended amount of 600-800 IU/day? Need I say more?
Moral of the story:
I don’t like being the bear of bad news, but the sun isn’t on your side for this one. At least for the winter, strongly consider taking a daily multivitamin or vitamin D supplement (~400 IU) and start incorporating more foods that are rich in vitamin D into your diet. Also, be sure to look for foods that are fortified with vitamin D such as, orange juice, yogurt, and a variety of cereals. Still not convinced to start popping the vitamin D to reach your daily goal? This vitamin may be doing a lot more beyond just bone health. Researchers are now investigating vitamin D’s associations with improved immune function and its impacts on overall decreased risk of type-2 diabetes and cancer. If that doesn’t get you thinking about your vitamin D intake this morning, maybe this will…
Important Sources:
6. Chen Z. L. et al. (2007). An evaluation of vitamin D in Fish: Is the vitamin D cotent adequate to satisfy the dietary requirement for vitamin D? J Steroid Biochem Mol Biol. 2007 March ; 103(3-5): 642–644. doi:10.1016/j.jsbmb.2006.12.010.
7. Sebastian R. S. et al. (2010). Fluid Milk Consumption in the United States. What We Eat in America: NHANES 2005-2006. Retrieved from http://www.ars.usda.gov/SP2UserFiles/Place/12355000/pdf/DBrief/3_milk_consumption_0506.pdf
8. Agricultural Research Service (USDA). Nutrient Database for Standard Reference, Release 25: Vitamin D. Retrieved from https://www.ars.usda.gov/SP2UserFiles/Place/12354500/Data/SR25/nutrlist/sr25w324.pdf
{ 15 comments… read them below or add one }
Supporting document: http://www.quickmeme.com/meme/3sv22s/
On a different note, I know there was a lot in the news this summer about the risks of taking vitamin D supplements and the USPSTF recommended against supplements for cancer and osteoporotic fractures: http://www.uspreventiveservicestaskforce.org/uspstf12/vitamind/draftrecvitd.htm
Do you have any thoughts on this?
Wow, that is quite entertaining. I had no idea that even existed–I will be sure to have some fun with that resource this semester!
Thank you for providing that document. From what I know so far in the literature, the evidence just isn’t there yet with cancer–However, I think it will be exciting to see if that might change in the next year as new research surfaces around vitamin D’s anti-proliferative anti-infalmmatory properties.
Also, if you dig in to some of the literature that was used as rationale in the IOM report, it brings up some issues as to what is considered an appropriate level for all health indicators–including bone health. I personally think that this population could certainly benefit from more sun exposure during the day (especially those who are home-dwellers or residing in nursing home communities) AND Vitamin D supplementation if they aren’t getting enough through their diet. I also don’t think you can dismiss the importance of strength training and balance exercises at this age to decrease risk of fractures/falls–so ideally, I think increasing vitamin D/calcium intakes AND strength training with this group are all things to consider. Given the contradicting evidence between the IOM and other vitamin D researchers in the field, this vitamin is tough one to really get a handle on!
Thanks again for the comment–keep them coming!
As an 80 year old male, doctor visits every six months and in good health, the posting gave me pause to think about my level of vitamin D. After reading the post explored how to determine levels of vitamin D. There is a test [25(OH)D or calcidiol] and my doctor has never suggested the option of a vitamin D test. Which will explore on my next visit.
Studies indicate older people who take Vitamin D seem to fall less often, probably due to better muscle function. My concern is that bone health, vitamin D and calcium go hand in hand, because the vitamin must be present for calcium to be absorbed from the digestive tract and that our body gets most of its vitamin D not from diet but from skin exposed to the ultraviolet B radiation in sunlight.
Yes–that is the test (it is the form of vitamin D that exists in circulation that best reflects the vitamin D that we are ingesting from the diet and the skin). I have heard this is a pricey test, so assuming that your vitamin D levels are within the RDA range (800 IU/day) you really shouldn’t be concerned.
Absolutely, the two vitamins work in concert. When blood calcium levels fall, parathyroid hormone (from the thyroid gland) signals vitamin D to act on bone cells to actually release calcium from the bone to maintain healthy levels in circulation (this is tightly regulated, and the process will only continue until calcium levels are back within normal range).
You’re also right about calcium absorption in the intestine–vitamin D will act on the intestine to promote the release of calcium from the intestinal tract.
Thanks for commenting–I’m glad this caused you start thinking about your own levels.
Amazing how taking vitamins regularly does get easier with age. Nothing like proof that a warm vacation is needed in the cold months.
Paige,
This is excellently researched, plus I like your style. As someone in sunny southern California, I don’t think I need to worry about my Vitamin D, but it was an interesting and important article. My one question, and I know I could google it, what is an IU? I have no medical background and my science is a bit lacking as well. Thanks for the post. It looks like you did a lot of research for this.
Margaret
Thanks for contributing Margaret! That’s a great question, and maybe I should have addressed this in the post. I agree, I think that there is some confusion about the different units that are seen with this vitamin.
IU stands for International Units– For vitamin D, 1 IU = 0.025 micrograms. IUs are just a more convenient way to express the amount but you may see some of the data reporting in micrograms.
If you see nmol/L–this refers to the levels reflected in circulation from a serum vitamin D test. In the CDC report that I provided a link for in this post–vitamin D deficiency is defined by a concentration <30 nmol/L. The recommended level is 40 nmol/L.
I hope this clears things up and I'm glad this has allowed you to appreciate the CA sun a little more!
Thanks Paige, this really did help. I appreciate the clarification and the length of your reply.
Margaret
Paige,
Thank you for bringing light (pun intended) to this topic! I think the importance of vitamin D is often overlooked, especially during the winter when it’s hard to get adequate vitamin D from sunlight. Did you read anything about the effects of vitD deficiency in the short-term?
I ask because last semester, I was having feelings of extreme fatigue and I got sick on three separate occasions. After several blood tests, my doctor found that my vitamin D levels were extremely low (thanks, Michigan…) and put me on a very high-dose vitamin D supplement. While I can’t say with certainty that the vitamin D was the only factor, I am certainly feeling a lot better now.
I’ve also read about vitamin D deficiency linked with anxiety and depression–did you read anything about this connection and whether or not it’s well established?
Good luck blogging this semester!
I’m really happy you brought this up because I was interested in this as well. There are definitely some cross-sectional studies out there that show significant associations. However, whether vitamin D deficiency is the cause of seasonal depression hasn’t been strongly established.
Shipowick CD, et al. (2009) studied the effects of vitamin D supplementation (5,000 IU/day) on depression in small group of women during the months of Jan-Mar. The supplementation was carried out for 8 weeks in a small group (n=9) of female nurses who had reported vitamin D deficiency. After the 8 weeks, there was a significant improvement in depressive symptoms. Obviously, this is a very small sample size, so there are definitely some limitations to these findings.
But…a 2011 review (G. Parker, H. Brotchie) of the literature suggests that there currently isn’t enough evidence to say that vitamin D supplementation can be used as a strategy to treat depression.
Personally, I think if you have felt better since making the change, keep doing it. I’m an advocate of doing what works for you. During the summer months, I don’t worry about my vitamin D levels. That said, during the short-term, I believe it is worth making the extra effort to maintain my levels by taking a daily supplement until March.
When I read your article, I thought about this video:
http://www.ted.com/talks/nina_jablonski_breaks_the_illusion_of_skin_color.html
It explains the evolutionary adaptation of skin to UV exposure and vitamin D..
I’m a huge fan of TED talks…thanks for sharing!
Well done! With Missouri’s bow to global warming I thought fifteen minutes on the patio in a swimsuit would supplement my supplement on some of our sixty degree days. Thank you for pointing out facts that the skin absorption rate changes with the seasons and I may be wasting my time.
Hi Paige! Thank you for the post. I thought it read well, but contained a few things that were a bit unclear. First of all, I wondered whether there were some figures for vitamin D conversion. E.g. how long would you have to stand in the sun during what month/sunlight intensity to obtain what dose of vitamin D? I also wondered what ’7-dehydrocholesterol’ and ‘precholecalciferol’ were and why there is a decline of the latter in the skin from August onwards. Is it due to lack of sun exposure or an unavoidable bodily mechanism? (Btw the link to the related study only leads to the Michigan library page.)
Hi Angela!
I will answer your second question first–don’t get too caught up in the names (in hindsight, I should have left these out of the post). The 7-Dehrdrocholesterol is actually what is present in the top layer of the skin. Upon sun exposure, this is what gets converted into the “pre-vitamin D” or precholecalciferol. After this, the pre-vitamin D then gets converted in to the active form of Vitamin D which can be used throughout the body (finally). As we age, the amount of the 7-Dhydrocholesterol in the skin declines. So, our ability to produce the pre-vitamin declines.
Now, hopefully you’re second question will make a little more sense. The UVB (not UVA) exposure is the source of the sun that is required for vitamin D synthesis. During the winter months, UVB is not nearly as strong. Consequently, there is much less conversion of vitamin D happening in the skin. This in combination with less overall sun exposure, and less “whole-body” exposure to sunlight can lead to a decline in vitamin D production.
As for how much vitamin D a person can produce in a given amount of time? Again, depending on latitude, season, time of day, and individual factors (age, race, skin type etc.) the conversion will vary. There is a study by Webb et al. (2008) that looks at this. In MI (42 degrees latitude) during the month of July, about 5 min/day = 400 IU of vitamin D. In December this goes up to about 20 min/day (this assumes you are exposing hands face neck arms and legs–which I find unlikely in December!).
Hope this helps! Thanks for reading!