May 14th, 2014 by Digestive Detective
In part one of this article series, I laid out the importance of vitamin D as an influential nutrient that impacts numerous physiological processes and the variety of health complications that can arise from deficiency. In addition, I outlined 3 primary causes that may contribute to deficiency. In this article, we'll delve deeper into other aspects of health that can result in vitamin D deficiency, or insufficiency, and what corrective measures you can take to improve your vitamin D status.
Poor Liver Function
The liver is a marvel of an organ, performing literally hundreds of functions in the body, namely those associated with protein synthesis, detoxification/biotransformation, cholesterol synthesis/transport, and biochemical conversion. It is in this area of biochemical conversion that the liver is essential to vitamin D status. When UVB rays are absorbed in the skin they are converted to a compound called 7-dehydrocholesterol. As the name implies, this molecule is dependent upon and derived in part from cholesterol in the body. Once synthesized through sun exposure, 7-dehydrocholesterol travels to the liver, where it is transformed by a liver enzyme known as 25-hydroxylase into 25-hydroxyvitamin D (25 OHD). This form of vitamin D is the version that physicians test in bloodwork to evaluate your vitamin D status.
In the presence of any form of liver dysfunction, the activity of the enzyme 25-hydroxylase may be impaired causing less effective conversion of 7-dehydrocholesterol to 25-hydroxyvitamin D. As such, less 25-hydroxyvitamin D may be produced resulting in a deficiency or insufficiency on a lab panel, and less active function of vitamin D in the body.
Liver dysfunction can be caused by a number of factors, including long-term alcohol consumption, prescription medication use, infection and inflammation. While overt liver conditions such as cirrhosis, hepatitis, or non-alcoholic fatty liver disease can greatly impair liver function, even minor influences such as high refined carbohydrate/sugar intake and poor detoxification pathways can prevent optimal liver function. Specific blood chemistry markers can help identify liver dysfunction and if found, health protocols that include consumption of sulfur-rich foods, certain amino acids, and removal of alcohol can improve function. Additionally, supplemental support in the form of herbal formulas and detoxification support powders can be employed to aide in proper liver capacity.
Poor Functioning/Lack of a Gallbladder
The gallbladder is a small pouch-shaped organ that serves to store and excrete bile for aiding in the digestion of dietary fats. Bile consists of bile acids (also called bile salts), cholesterol, bilirubin (a breakdown product of red blood cells) and minerals such as potassium, sodium, and copper. Bile acts as a kind of detergent that emulsifies the fats you take in through your meals. Unfortunately issues with gallbladder function are relatively common, and removal of the organ is among the most commonly performed surgical procedures conducted each year. The absence of a gallbladder can lead to a number of health considerations which I've outlined in a prior article. Among these considerations, is the absorption of fat soluble vitamins such as vitamin D. Without a full-functioning gallbladder, dietary fat absorption will be impaired, and poor absorption of vitamin D can result despite your best efforts with consumption of vitamin D-rich foods. If you are among the thousands of individuals who have had their gallbladder removed or experience a sub-optimal functioning gallbladder, then proactive steps are crucial to ensure ideal absorption of dietary fats and fat soluble vitamins. To learn how you can support gallbladder function and enhance vitamin D and dietary fat absorption, check out this article for detailed nutrition and supplement support options.
You may be familiar with body mass index (BMI) from your annual physical or an appointment with a personal trainer. BMI is a standardized measurement of weight that categorizes the ranges for "normal" weight, overweight, and obesity. Systematic reviews and meta-analyses have demonstrated an association between high levels of excess weight (as measured through body mass index) and vitamin D deficiency. In a 5 year study of 12,927 adults, data from the National Health and Nutrition Examination Surveys showed that "overweight and obese individuals were 24% and 55%, respectively, less likely to have a 25-hydroxyvitamin D level of 30 ng/mL or greater (the bottom-end range below which indicates deficiency) compared with their normal-weight counterparts."
Another multi-centre cross-sectional European study of adolescents that included over 1,000 teens showed that BMI and body fat % were highly related to 25(OH)D concentrations.
The studies seem to indicate that the higher the level of excess weight, the greater impact on vitamin D levels. While BMI categorized as overweight appears to have an association, obesity level (defined as BMI over 30) seems to have an even greater influence on not only circulating vitamin D levels, but the effects of vitamin D supplementation on correction of deficiency. In another analysis of multiple cohort studies (21 adult cohorts with up to 42,024 participants) researchers developed a score for BMI utilizing 12 BMI-related SNPs (single nucleotide polymorphisms - genetic variants) to produce an instrument for BMI and four SNPs associated with 25(OH)D. Upon analysis, researchers concluded:
"The association between obesity and vitamin D status was remarkably consistent across the different populations included in our meta-analyses, being apparent both in men and in women, and in the young and older cohorts alike. On the basis of a bi-directional genetic approach that limits confounding, our study suggests that a higher BMI leads to lower 25(OH)D."
These studies point to a clear need for weight management in the improvement of vitamin D deficiency where appropriate, while other studies add a layer of complexity surrounding supplementation. In individuals identified as being vitamin D deficient, supplementation is often recommended and warranted; however, evidence exists that obese individuals may require even higher levels of supplementation than their normal weight counterparts. In a study conducted by European researchers, results demonstrated that subjects with high BMI had lowest baseline 25(OH)D levels and also the smallest increase after supplementation. Research published in the American Journal of Medicine and the European Journal of Nutrition suggest that overweight and obese patients with hypovitaminosis D (deficiency) might require higher doses of vitamin D to achieve vitamin D repletion compared with individuals with normal body weight.
These factors add to the complex nature of vitamin D deficiency and therefore to the resolution of deficiency. While intake and sun exposure are the initial mechanisms that are often addressed, the research and physiology behind vitamin D metabolism provide additional factors for consideration. In part 3 of this series, we'll explore the delicate balance between vitamin D and other micronutrients and discuss how supplementing with vitamin D alone can actually make matters worse.