Vitamin D is emerging as a critical nutrient for many body processes. In addition to helping to form and maintain strong bones, vitamin D controls more than 200 genes. Vitamin D deficiencies can lead to osteomalacia, which results in muscular weakness in addition to weak bones. Vitamin D insufficiency has been linked to diseases such as high blood pressure, tuberculosis, rheumatoid arthritis, cancer, periodontal disease, multiple sclerosis, chronic pain, seasonal affective disorder, peripheral artery disease, metabolic syndrome, cognitive impairment, Parkinson’s, and several autoimmune diseases including type 1 diabetes. The discovery that vitamin D regulates the immune system, controls cancer cell growth and regulates the blood pressure hormone renin, provides an explanation for why vitamin D sufficiency has been observed to be so beneficial in the prevention of many chronic illnesses. A recent meta-analysis of 18 studies including almost 60,000 people found a 7% reduction in mortality in those who took daily vitamin D supplements in dosages ranging from 300-2000IU.
When researchers monitored the vitamin D levels, blood pressure and other cardiovascular risk factors for 5 years, they found that those people with low levels of vitamin D had a 62% higher risk of a cardiovascular event than those with normal vitamin D levels. Low levels of vitamin D have been implicated in hypertension, elevated VLDL triglycerides, and impaired insulin metabolism. Vitamin D deficiency may contribute to the wide set of disorders associated with metabolic syndrome (syndrome X), as well as to polycystic ovarian syndrome. In a study published in 2004, the authors saw a 60% improvement in insulin sensitivity in healthy, vitamin D replete adults — and concluded vitamin D was more potent than two prescription medications commonly used to treat type 2 diabetes.
Obesity and vitamin D: Overweight and obese are at increased risk for Vitamin D deficiency. Since vitamin D is fat-soluble, it can accumulate in body fat, making it less available to other parts of the body. There are several studies that have confirmed the link between excess fat and vitamin D deficiency. Additional studies have identified an inverse association between vitamin D status and diabetes as well as the metabolic syndrome. Repletion can improve insulin sensitivity and may assist with weight loss in those who have insulin resistance. Obese individuals are only able to increase their blood levels of vitamin D to 50% compared to individuals with normal weight.
Prevalence and screening: The prevalence rate of vitamin D deficiency has been reported to be 36% of otherwise healthy individuals, and is currently recognized as an epidemic in the United States. Historically, exposure to the sun used to give us all the vitamin D we needed. We would require the exposure of arms and legs without sunscreen for 10-30 minutes, and those with darker skin would require longer exposure times. Applying sunscreen with an SPF factor of 8 reduces production of vitamin D by 95%. Dietary sources of vitamin D are limited to fatty fish and vitamin D-fortified foods and a recent survey of the vitamin D intake in the United States revealed that neither children nor adults are receiving the recommended intake of vitamin D.
Populations who have been traditionally considered high risk for vitamin D deficiencies include the elderly, obese individuals, exclusively breastfed infants, individuals who have limited sun exposure or have dark skin, or individuals who avoid the sun and apply sunscreen regularly. Also, at risk are individuals who have fat malabsorption syndromes (e.g., cystic fibrosis, gastric bypass) or inflammatory bowel disease (e.g., Crohn’s disease).
Due to the high prevalence, many clinicians feel that Vitamin D levels should be measured routinely as part of an annual physical, and especially any individual who are identified in the high risk category should be screened.
Diagnosis: We can screen for vitamin D deficiency through a blood test. The optimal levels for 25-hydroxyvitamin D in the blood are controversial. Historically, levels below 32nmol/L were considered a risk factor for the development of rickets and osteomalacia. However the avoidance of long latency diseases such as cancer and diabetes may require levels as high as 80nmol/L. The lab method used to measure the blood levels need to be considered when interpreting the results, where difference of up to 30% can be seen what lab method utilized. as well as seasonal variation. For example, the lowest levels are found in Feb and March.
Treatment: In the past, blood levels above 38nmol/L were considered normal. However, researchers now believe that blood levels of between 80 and 100 nmol/L should be considered the optimal level. Researchers and experts are also calling for a change in the RDI recommendations to a minimum of 800IU for children and adults. It’s recommended that obese patients take 1000-2000IU/day because of the decreased bioavailability to avoid deficiency. In an obese patient diagnosed with a deficiency, recommended treatment is 50,000 IU every week for 8-12 weeks and retested for another 8-12 weeks if the retesting result is <75nmol/l.>Summary:
Vitamin D is emerging as a critical nutrient for long term health and longevity. Given the prevalence of the deficiency and significance to health, screening for vitamin D levels should be considered for everyone, but especially for those at high risk or may be symptomatic, ie overweight/obese, hypertension, chronic pain, metabolic syndrome. We can easily screen for deficiency by measuring serum 25-hydroxyvitamin D. Although the optimal levels are still controversial, researchers suggest that levels ~ 80nmol/L may be required to avoid the long latency diseases such as cancer and diabetes. Sun exposure is an important source for Vitamin D, however, dietary intake of fatty fish and supplements can provide additional nutritional support. Higher levels of supplementation are recommended for those who may have absorption or bioavailability issues such as the elderly, obese, inflammatory bowel disease, cystic fibrosis or gastric bypass. Deficient patients should be retested to assure adequate treatment.
Written by Sooji Rugh, MD – GreenLite Physician