April 30th, 2014 by Digestive Detective
Vitamin D is an extremely important nutrient whose functions are only now beginning to be more fully understood in the scientific community. Originally, when first discovered, vitamin D or calciferol was identified primarily for its function in calcium metabolism (as the name "calciferol" demonstrates). Since then, a growing body of research has linked vitamin D to functions associated with gene regulation, neurotransmitter balance, bone metabolism, muscle function/hypertrophy, blood pressure regulation, immune function, insulin secretion/blood sugar regulation, and cell differentiation, proliferation and growth.
As the research continues to demonstrate the wide range of influences that vitamin D exerts on the body, it has become clear that a deficiency of the vitamin can result in serious health complications. Research has exhibited vitamin D deficiency to be strongly associated with all cause mortality - that is to say death by all causes (cardiovascular disease, cancer, respiratory disease, etc.). It has been suggested that vitamin D deficiency may influence the development of diabetes, cardiovascular dysfunction and autoimmune diseases as well. While the dangers of deficiency seem to grow daily, an "epidemic" of vitamin D deficiency has emerged among the population, with estimates that more than one billion people worldwide are either deficient or insufficient and numerous studies reporting that 50-100 percent of the elderly men and women in the US and Europe are vitamin D deficient.
My guess is the reason you found this article is that you or someone you know has been told by their doctor that they are deficient in D and are trying to determine why and how that may have occurred. Perhaps you were simply told by your physician that you "need to start taking vitamin D" with little to no explanation as to why. While supplementation with vitamin D may be necessary, its an unfortunately common approach to simply pop a pill (be it prescription or supplement) and not truly seek out the underlying cause. This three-part article is designed to help you do exactly that: understand the many reasons why you may be deficient in the first place, so you can take corrective action in that area and not simply slap a vitamin D-laced band-aid on your "wound" and go about your day (besides, after you stop supplementing, will your vitamin D level remain in adequate range if intake is not the main reason you were deficient in the first place? The answer to that question lies below.)
Lack of Sun Exposure
The primary means of obtaining vitamin D is via direct exposure to sunlight. The high rates of deficiency are thought to be caused, in part, by insufficient daily sunlight exposure especially in northern latitudes. Season, time of day, length of day, cloud cover, smog, skin melanin content, and sunscreen are among the factors that affect UV radiation exposure and vitamin D synthesis. Sufficient amounts of vitamin D are thought to be obtainable by direct sunlight on at least 30% of exposed skin for 5 to 30 minutes between 10 a.m. and 3 p.m. three times per week. This degree of exposure provides the body with 1000 IU of cholecalciferol (vitamin D3 - one of the main forms of the vitamin). Individuals with darker skin and the elderly may require longer exposure to reach the same levels of vitamin D synthesis. If you are currently deficient, your first course of action should be to schedule this amount of sun exposure into your life on a weekly basis.
Lack of Dietary Intake
The second reason that you may be deficient in vitamin D is simple: you're not consuming enough in your diet. Very few foods contain vitamin D because of the body's ability to obtain vitamin D through sun exposure. There are a few foods that are good sources however, including:
- Cod liver oil 10,000 IU / 3.5 oz
- Salmon 511 IU / 4 oz
- Herring 175 IU / 3 oz
- Tuna 93 IU / 4 oz
- Liver (beef) 40 IU / 3 oz
- Eggs 43 IU / egg
- Shitake Mushrooms 20 IU / ½ cup
The Recommended Dietary Allowance for vitamin D, which assumes minimal sun exposure, suggests an intake of 600 IU of vitamin D for children (age 1 and older), adolescents, and adults including women who are pregnant or lactating. Recommended intakes increase to 800 IU of vitamin D for adults older that 70 years of age. Of course your food intake is only as good as your ability to digest it when it comes to absorbing nutrients properly...
Poor Digestive Function
Despite your best efforts with intake, if you experience digestive dysfunction and impaired nutrient absorption, the vitamin D you consume won't get to the cells in the body to impart its effects. As it stands, only about 50% of dietary vitamin D is absorbed (under ideal circumstances). Factor in some form of digestive disturbance and that percentage likely falls even lower. The majority of vitamin D is absorbed in the distal small intestine, meaning that the nutrient must travel through the stomach, duodenum, and jujenum (both higher up in the small intestine) before reaching the more distant location in the gut. If any form of digestive condition is present such as dysbiosis, SIBO, IBS or others, the likelihood that you're absorbing adequate amounts of D is diminished. In inflammatory bowel diseases such as Crohn's and ulcerative colitis, vitamin D deficiency has been shown to occur as a result of malabsorption and general bowel intolerance. Celiac disease patients also often experience deficiency as a result of impaired absorptive capacity. As a fat soluble vitamin, D is absorbed from a micelle (lipid molecules that arrange themselves in a spherical form in aqueous (water-based) solutions) in association with fat and with the aid of bile. Poor fat digestion, as evidenced by these types of bowel movements, results in poor absorption and transport of fat soluble vitamins such as D via the micelles.
In part 2, we'll explore this dietary fat connection even further, as well as reveal the main organ that may be at the very center of your vitamin D deficiency.
How is your vitamin D level? Have you been tested recently and aren't sure what to make of the results or what steps to take next? Comment below and I'll share my insights into your specific situation.