I have mixed feelings about Fall’s time change—both great and glum. What’s great? Having that one 25-hour day. What’s glum? Short days with too much darkness!! And with all this darkness, it leads me to wonder, is “falling back” bad for your health? It’s quite possible, considering we’re down to about 9-11 hours of daylight per day, depending on where you live in the United States.
With minimal sunlight, people’s vitamin D levels are certainly lower during the winter months. Not only is the amount of time you’re exposed to the sun much less, but if you are exposed, the sun’s rays are also weaker. During the winter months, the further away from the equator you are, the more of an angle the sun's rays hit the atmosphere. This means less UV light is available for your body to produce vitamin D.
Vitamin D deficiency has been associated with poor immune function, poor cardiovascular health, depression, inflammatory bowel disease, osteoporosis and hormone imbalance (1).
Along with vitamin A and thyroid hormone, vitamin D regulates the DNA of some cells to favor maturation into specific cell types. This is important in orchestrating tissue development in the fetus and growing child.
As you can imagine, if darker days result in less vitamin D circulating through your body, your health will be affected.
Vitamin D and Seasonal Affective Disorder
One common winter disorder is SAD—Seasonal Affective Disorder. This mood-related disorder is a form of depression and is very real and severely debilitating. Symptoms of SAD are generally worse in January and February and begin to disappear as the days lengthen in the spring. Research does seem to show a link between symptoms of depression and low levels of vitamin D in the blood. However, research hasn’t yet shown clearly whether low vitamin D levels cause depression, or whether low vitamin D levels develop because someone is depressed (2).
Did You Know? More people break their bones in the winter in both the Northern and Southern hemispheres than other times of the year. Why? You guessed it…some researchers believe it’s because people have lower levels of vitamin D in their bodies during this time (3). Most people know calcium is important for strong bones, and just as important is vitamin D. You need vitamin D to help absorb calcium.
Vitamin D Sources
Because there are only small amounts of vitamin D in food, there are only two sure ways to get enough vitamin D:
How Do I Know If I’m Deficient In Vitamin D?
A doctor measures vitamin D by testing your 25(OH)D level. Getting this blood test is the only accurate way to know if you’re deficient or not.
Recommended Levels of Vitamin D
Scientists don't yet know the optimal daily dose of vitamin D, and recommendations vary depending on who you ask. Here are recommendations for adults from three different credible entities.
The Vitamin D Council recommends 5,000 IU/day
The Food and Nutrition Board recommends 600-800 IU/day
The Endocrine Society recommends 1,500-2,000 IU/day
The current daily recommendations set by the Food and Nutrition Board are conservative, so you don’t have to be concerned about toxicity if you take more than that amount. In fact, it takes a lot of vitamin D to develop a toxicity—40,000 IU per day for a couple of months or longer, or a very large one-time dose. A good starting point is to test your vitamin D levels via a blood test, and adjust your dosage based off the results (4).
Fat-Soluble Vitamin D
Vitamin D is a fat-soluble vitamin, which means your body stores it for long-term and has a hard time getting rid of it if you take too much. Here's the difference between a water-soluble and fat-soluble vitamin. If you purchase a vitamin D supplement in liquid form, it should be suspended in a healthy fat, such as olive oil or MCT oil, in order to boost its absorption. I like this liquid vitamin D. You can also take your vitamin D with food that contains fat, such as nuts, avocado, olives and full-fat dairy.
Bottom Line: Shorter, darker days means less exposure to sunlight which reduces the amount of vitamin D circulating through your body and can affect your health. Get tested. Make sure yourself, your kids, your family, and your friends receive enough vitamin D during the winter. It's a nice excuse to get outside in the middle of the day when the sun is the strongest.
In Health and Happiness,
Kelly Harrington, MS, RDN
Registered Dietitian Nutritionist for Healthy Goods
1. Vitamin D Council. Health Conditions.
2. Kjaergaard M, Waterloo K, Wang K etc al. Effects of Vitamin D supplement on depression scores in people with low levels of serum 25-hydroxyvitamin D: nested case-control study and randomised trial. Br J Psychiatry. 2012 Jul 12.
3. Avenell A, Gillespie WJ, Gillespie LD, O’connell D. Vitamin D and vitamin D analogues for preventing fractures associated with involutional and post-menopausal osteoporosis. Cochrane Database Syst Rev. 2009;(2):CD000227.
4. Vitamin D Council. How do I get the vitamin D my body needs?