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:
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:
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.
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…
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