Your kidneys are hard-working organs that filter approximately 200 quarts of blood daily to eliminate roughly two quarts of waste products from your body. Too much vitamin D can place a strain on these organs and may provoke kidney stones. On the other hand, vitamin D deficiency is associated with chronic kidney disease and doctors use vitamin D supplements to treat the disease. If you have kidney disease, if it runs in your family or if you have experienced a kidney stone, talk to your doctor before taking vitamin D supplements.
Kidney Basics
Each of your kidneys contains approximately 1 million nephrons --- tiny structures that filter waste matter and water from your blood and convert it into urine. Your kidneys also produce three essential hormones: erythropoietin, which stimulates the production of red blood cells; rennin, which helps to control your blood pressure and calcitriol, the active form of vitamin D. Most kidney diseases involve damage or destruction of the nephrons.
Vitamin D Sources and Dosage
Very few natural foods contain vitamin D, but you can get it from exposure to sunlight or from fortified foods and supplements. Your body cannot use any of these forms of Vitamin D directly. First, your liver must convert them to a different form of vitamin D called calcidiol. Then your kidneys convert the calcidiol to calcitriol. While vitamin D is necessary to help your body absorb calcium, reduce inflammation and regulate cell growth, you can get too much of it. For adults between the ages of 19 and 70, the National Institutes of Health recommend 600 IU of vitamin D daily. People over the age of 70 need 800 IU per day. It is unlikely that you will overdose on vitamin D from sun exposure because sustained heat on your skin degrades your body's production of the vitamin from sunlight. You can get too much vitamin D from supplements. Adults should not take more than 4,000 IU per day.
Vitamin D Risks
Because vitamin D helps your body to absorb calcium, excess intake of vitamin D may cause the level of calcium in your blood to rise above normal. This may cause crystals to form inside your kidneys and the crystals may converge into painful kidney stones, which may block the flow of urine from your kidney and damage the organ. Elevated calcium levels also can interfere with your kidneys' ability to filter wastes from your blood and may damage them over time, even if you don't develop kidney stones. In extreme cases, permanent damage may require dialysis treatment to replace lost kidney function and may eventually lead to death. Symptoms of vitamin D toxicity include nausea, vomiting, weakness, confusion, irregular heartbeat, loss of appetite and constipation.
Vitamin D Kidney Benefits
While too much vitamin D taxes kidney function, a carefully regulated amount can help patients with kidney disease. In a 2008 study published in the "Clinical Journal of the American Society of Nephrology," researchers at the St. Louis University Medical Center found a correlation between chronic kidney disease and vitamin D deficiency. They advocate treatment with vitamin D supplements to correct the imbalance and help with bone abnormalities associated with the progression of this disease. Similarly, in a 2007 study published in "Current Opinion in Nephrology and Hypertension," researchers at the Washington University School of Medicine found that vitamin D supplements increased the survival rates of patients undergoing dialysis.
References
- National Kidney & Urologic Diseases
- Office of Dietary Supplements National Institutes of Health: Vitamin D
- "Clinical Journal of the American Society of Nephrology"; Vitamin D and Kidney Disease; Wisam Al-Badr and Kevin J. Martin; 2008
- National Kidney & Urologic Diseases
- PubMed.gov: Vitamin D and outcomes in chronic kidney disease; S. Cheng and D. Coyne; 2007
- MayoClinic.com: Hypercalcemia
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