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|Nutrition and You: Got Sunshine?|
Recent studies have revealed a surprising number of potential additional effects of vitamin D. For example, adequate vitamin D status is important for muscle performance (e.g., it may help prevent falls) and to help regulate the immune system. In addition, people with adequate blood levels of vitamin D may be less likely to develop diabetes, cardiovascular disease, and several types of cancer, including colon, prostate, and breast.
Its SourceFor most people, there are three ways to get vitamin D: (1) sun exposure, which converts pre–vitamin D in the skin to a usable form; (2) food sources, which include oily fish (e.g., salmon, sardines, or tuna) and fortified milk products/cereals; (3) oral vitamin D supplements. This can present a challenge for home parenteral and/or enteral (HPEN) consumers. Some of you may not feel like going outside, and many people cannot get enough sun anyway, at least part of the year; the food sources are limited and may not be tolerated, or perhaps you just cannot eat; and finally, vitamin D supplements require absorption by the GI tract — which may be a problem.
Measuring ItAssessing your blood level of vitamin D is the only way to determine if your intake from sunshine, food, and/or HPEN is adequate, and screening blood levels of vitamin D should be part of the routine blood tests for everyone. When evaluating vitamin D status, your clinician should order a test for 25-hydroxy vitamin D levels. Although there is no agreement on the optimal level for good health, a general guideline is that a plasma hydroxy vitamin D > 30 ng/mL is desirable, while Dr. DeLuca and others suggest a level of 40-60 ng/mL may be associated with disease prevention.
You are getting enough vitamin D when your 25-hydroxy vitamin D levels reach the desired level. How you reach these numbers depends on many factors, including your age, your size, how much you can eat and absorb, and how much sun exposure you get. Several organizations have recommended intakes for healthy populations (i.e., those with adequate fat digestion/absorption and liver and kidney function necessary to activate vitamin D from sunshine or food). The 1997 Recommended Dietary Intake (RDI) suggested an adequate intake is 5 mcg (200 IU) from birth to age 50; 10 mcg (400 IU) ages 51–70; and 15 mcg (600 IU) for age > 71. The American Academy of Pediatrics later recommended 10 mcg (400 IU) per day for pediatric and adolescent populations.
Now, emerging science tells us that the recommendations we have always followed for the amount of vitamin D are really too low. The RDI is being updated, and current recommended amounts for adults are at least 25 mcg (1000 IU) per day.
The amount recommended is based on oral/enteral intake. Enteral feedings contain vitamin D, but an oral supplement may still be required. An adult parenteral multiple vitamin supplement (e.g., MVI-12) typically provides 5 mcg (200 IU) vitamin D per day, while the pediatric formulation provides 10 mcg (400 IU). This may or may not be adequate to meet the consumer’s needs. The only way to really determine if your vitamin D intake is adequate is by testing your 25-hydroxy vitamin D levels. If you are an HPN consumer and your vitamin D levels are low, you may need to bring them up with UV exposure, as there is no parenteral form of vitamin D other than in the intravenous multivitamin.
As mentioned above, vitamin D has many functions, including promoting calcium absorption in the gut and maintaining adequate serum calcium and phosphate concentrations to enable normal mineralization of bone. Vitamin D also plays a role in bone growth and bone remodeling by osteoblasts and osteoclasts, and protects against osteoporosis in older adults. We now know that vitamin D has other roles in health, including regulating the immune system and reducing inflammation.
Are You at Risk for Deficiency?People who may be at risk for vitamin D deficiency are those who have little exposure to ultraviolet light from the sun (or a tanning bed), and people who consume little or no foods that contain vitamin D, such as oily fish (i.e., salmon, sardines, mackerel, tuna), fish oil, or foods fortified with vitamin D (like milk, milk products, and cereals). In addition, certain medications (such as glucocorticoids and antiepileptic drugs) can reduce your vitamin D, and certain conditions (such as advanced /chronic liver or kidney disease) can reduce the conversion of vitamin D to its active metabolite in the body.
Adults on home enteral nutrition receive the Recommended Dietary Intake (RDI) of 400 IUs or more per day in 1500 ml of commercial formula. Children on enteral nutrition receive the minimum RDI (400 IUs) in 1000 mL of formula (ages 1 to 8), and 1500 ml of formula (ages 9 to 13). People who receive home parenteral nutrition receive the parenteral equivalent of the RDI of vitamin D in their daily multivitamin infusion (200 IUs adults, 400 IUs children). However, many researchers feel that the RDI of vitamin D may be insufficient, and that both adults and children may benefit from a higher amount. How much more should be based on the individual’s level of active vitamin D, which is measured by their level of serum 25-hydroxy vitamin D. At the 2009 parenteral micronutrients conference, Hector DeLuca, MD, a world expert on vitamin D, recommended 25-hydroxy vitamin D serum levels at a minimum of 30 ng/ml and no more than 100 ng/ml for all adults. This level is recommended for children, as well.
To determine your risk of vitamin D deficiency, ask yourself:
What About Toxicity?
It is possible to get too much of a good thing? An excess of vitamin D (hypervitaminosis D) can cause high blood concentrations of calcium (hypercalcemia), which can cause overcalcification of the soft tissues, heart, and kidneys. It can also produce kidney stones, and can result in hypertension. Hypervitaminosis D symptoms appear several months after excessive doses of vitamin D supplementation.
What Should You Do?
Ask your physician to check your status by measuring your serum 25-hydroxy vitamin D level. If you are deficient (below 30-100 ng/ml), you and your physician can decide the best method of replenishing vitamin D, whether that is adding an oral or enteral vitamin D supplement. (IV vitamin D is not available as a separate product.)
Since vitamin D has multiple functions in the body, it is worth determining your vitamin D status whether you are an HPEN consumer or a care provider to ensure you maintain a healthy level.
This column has been compiled and reviewed by Carol Ireton-Jones, PhD, RD; Laura Matarese, PhD, RD, LDN, FADA, CNSD; Cheryl Thompson, PhD, RD, CNSD; and Marion Winkler, PhD, RD, CNSC. Their next column will include risk factors for vitamin D deficiency, and benefits and risks of vitamin D supplementation.
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