As I am writing this, the sky is utterly grey and the season's first snow is falling from the sky. Though I had already planned on writing about vitamin D this week, today's weather gives me a greater sense of urgency when wanting to discuss its significance. Vitamin D is best known for its association with the sun and, as the amount of sunlight wanes and our layers of warm clothes increase this time of year, now is prime time to dig into vitamin D.
A study from 2012 shows that vitamin D deficiency affects 50% of the worldwide population, with other studies suggesting about a 40% deficiency rate seen in U.S. adults. Many suggest even higher deficiency rates for different populations, including the elderly, infants, those with darker skin complexions, certain medical conditions and those with religious beliefs that preclude more covered skin. There is probably an even higher rate of deficiencies that have not been diagnosed, or even sub-clinical deficiencies for a large percentage of the population. This would mean their blood values of vitamin D may not be low enough to show up as a clinical deficiency, but are too low to support robust long-term health. For a vitamin that comes freely from the sun, this is a staggering rate of deficiency to me. I would venture to guess that there is even more prevalence of insufficient vitamin D now that people are staying at home all the time!
The Role of Vitamin D
Vitamin D plays a number of physiological roles, often acting as hormone to influence various systems and cellular functions in the body. Vitamin D is probably best known for its impact on bone health, as it is needed for proper absorption of calcium and balancing calcium and phosphorus levels. Besides supporting healthy bones and teeth, it also has been linked to heart health, improved immune function and resistance to cancer, blood sugar regulation and thyroid function, as well as mood and mental health (including Seasonal Affective Disorder). With all of these roles it can play in the body, it is easy to see why we must address the high rate of deficiency in this vitamin.
Having sub-optimal vitamin D levels over a long period of time can lead to issues and disruptions in all of the systems mentioned above. Vitamin D deficiency also increases mortality, as an independent risk factor, so addressing deficiency is clearly important to address long-term health, but deserves attention in the short-term as well. If vitamin D is extremely low, especially during periods of growth such as childhood, one could develop conditions such as tetany or rickets. Tetany causes muscle twitching and spasms, while rickets causes softening and weakening of the bones, which can lead to problems with growth and even walking. Rickets is rarely seen in the developed world, as most milk is now fortified with it. However, inadequate intakes that are enough to prevent rickets, but not enough to promote optimal health, are very common. Getting too much vitamin D, on the other hand, can also cause health problems such as soft tissue calcification or excess calcium in the blood. Excessive vitamin D would typically be caused by over-supplementing, however, not from sunbathing too much.
The Sunshine Vitamin
Vitamin D has gotten its nickname as "the sunshine vitamin" due to the fact that we can get a significant amount from sun exposure, as our bodies convert the UV light into this vitamin when it comes into contact with our skin. But it is just that easy? A little bit of sun and you get all the vitamin D you need? Well, it is a bit more complicated than that.
There are some special considerations when determining if you are able to get adequate vitamin D through sun exposure or if you may need to amend the sunshine with food and supplements. One of these is the timing and quality of sun exposure. For the optimal amount of sun for vitamin D synthesis, you would want as much skin exposed to the sun as possible during midday (around the noon hour). This would mean that if you were mostly clothed or if your sun exposure was early in the morning or later in the afternoon, you may not be optimizing your sun exposure for vitamin D. The amount of sun needed for optimal vitamin D synthesis depends on your skin tone and sun tolerance.
Those with lighter skin tones need less sunshine to synthesize vitamin D, while darker skin tones need more, as the melanin in the skin inhibits the conversion of UV rays to vitamin D. Lighter-skinned people can get adequate sun for vitamin D if they sunbathe or have some skin exposed, just up until they begin to turn pink. If you start to burn, you have overdone it, and in fact, have maxed out how much vitamin D you can make at that point. This could be 10-30 minutes, depending on how sun tolerant someone is. For darker-skinned people, they would likely need a much longer stint in direct sunlight, which could even be up to an hour or more, to synthesize adequate amounts of vitamin D in the skin.
One kicker with sun exposure, no matter the melanin content of the skin, is that time of year and latitude will affect the quality of sunlight for making vitamin D. For example, those in Northern climates during the winter time will absorb less vitamin D from the sun, even if they do get out in the sunshine midday, as the UVB rays are not as strong during the winter. Also, if you are in a colder climate, more of your body will be covered due to the weather, so less skin is exposed overall, decreasing the vitamin D synthesis potential at that time as well.
Besides melanin and clothing--especially dark clothing-- other barriers that block UV rays, thus preventing vitamin D synthesis in the skin, include: sunblock, shade, clouds, air pollution, and windows. So, if you had any hopes of throwing on sunblock and hitting the beach to soak up some vitamin D, you will need a new strategy. To balance the need for direct sunlight on the skin with the need to not burn, get your midday sun for a shorter amount of time, stopping before you start to get pink. Then, you can use some sort of sun protection such as shade, clothing, or a chemical-free sunblock to prevent burning if you would like to continue to enjoy the outdoors midday. Sitting in the window on a sunny day or sunbathing on a cloudy day won't cut it, either; finding other ways to get your vitamin D needs met may be necessary if you have limited access to midday sun on a regular basis, burn easily, or if you live in a Northern climate during the winter.
What about winter?
If those of us in Norther climates can't get enough sunlight in the colder months for adequate vitamin D synthesis, then what do we do? We would take a lesson from those who have lived in these areas for centuries, and turn to food. There are a few food sources of vitamin D3 (the more bioavailable form of vitamin D), which are all ancestral, animal-based foods. Having adequate fat in the diet is necessary for proper vitamin D absorption from food sources, so consuming a diet rich in unprocessed fats is a good place to start.
Animal foods have provided vitamin D to those in Northern, colder climates well before there were capsules available to buy at the store and it is time to consider these the superfoods that they really are.
Some of the best food sources of vitamin D3 include:
It is important to remember that the animals must be raised outdoors, with plenty of sun exposure themselves, for the food they provide to have adequate amounts of vitamin D. There are many foods that are enriched with vitamin D, such as almost all milk sold in the U.S., but obtaining as much of your vitamin D intake from food sources as you can is ideal.
Who is at risk for deficiencies?
As discussed above, there are huge amounts of the world's population that are deficient or insufficient in this essential vitamin. Though we can synthesize vitamin D from the sun and have multiple food sources available, this continues to be worldwide health issue, which some refer to as "pandemic" level. Some populations are more at-risk for this deficiency, however. Because the sun is once of our best sources, those with limited sun exposure are at a very high risk of deficiency, as well as those who would be unable to get adequate amounts from the diet, such as those consuming a modernized diet.
Here are some of those groups most at-risk:
Do I need a supplement?
For those in any of the high-risk groups listed above, supplementation of vitamin D is often needed to have adequate levels in the body. With indoor lifestyles, diets rich in processed foods, and chronic health conditions afflicting so many, the modern way of living does not make it easy for almost anyone to get enough vitamin D through sun or food. Though supplements are frequently necessary, I do encourage starting with lifestyle modifications as much as possible and then supplementing if needed.
If you feel you are at-risk for low vitamin D, it is definitely worth getting labs drawn to determine your exact vitamin D status and supplementing as needed after that. The most common test for this is the 25(OH)D test (calcidiol), which optimally would fall between 30-50 ng/mL. There are other tests that can help determine your vitamin D status, and other factors that could cause an altered 25(OH)D result besides insufficient sun or dietary intake (such as chronic inflammation or inadequate calcium intake), but getting this drawn is a good place to start. Getting further assistance from your healthcare provider is, of course, part of the equation here as I am not giving you healthcare advice, just general information.
If you are deficient, as proven by labs, then supplementing may be necessary for you, as lifestyle and diet have likely not met your body's needs. When choosing a vitamin D supplement, no matter the dose, look for those labeled vitamin D3 for the best absorption. Choose those that come from natural sources, such as lanolin or cod liver, rather than synthetic sources. A vitamin D3 supplement with vitamin K2 added will also help with absorption, and these are becoming increasingly easy to find. Cod liver oil, either in liquid or capsules, also provides vitamin D in a food source, along with vitamin A and omega 3 fatty acids. Though this is a good choice for all of these reasons, the amount of vitamin D provided may vary by brand and processing method, so do some research before purchasing, especially if you need a higher dose of D3 due to a deficiency. If you are looking to consume a high dose of vitamin D3 (over 2000 IU) for whatever reason, then you should be getting your labs checked regularly by your doctor to avoid excessive vitamin D intake.
As we head into colder months, now is an essential time to shine some light on vitamin D in your life. Evaluate if you do (or even can) get enough from the sun these days, look at your intake of vitamin D-rich foods, and consider if getting labs drawn and adding a supplemental vitamin D3 source may be right for you. What better time to ensure you have the happiest and healthiest winter possible?
Brine & Broth
I am a nutritionist in Southwest Wisconsin, focused on traditional, nutrient-dense foods. My goal is to provide you with simple and delicious recipes that fit into real life, and information for choosing healthful real foods. Enjoy!