DaVita Espanol

DaVita.com > Kidney disease education > Diet And Nutrition > Diet Basics > Vitamin D And Chronic Kidney Disease

Vitamin D and Chronic Kidney Disease

Written by DaVita renal dietitians Helen Dorough and Sara Colman

We do get vitamin D from the ultraviolet (UV) rays of the sun, but not all sunlight is equal. The amount of UV rays absorbed depends on where you live, the time of day, the season, whether it’s cloudy and if you’re using sunscreen. People who live in sunny areas at lower latitudes can get enough vitamin D with about 10 to 15 minutes of sun exposure three times a week. People living at higher latitudes, such as Detroit, St. Paul, Boise and Boston will not get enough vitamin D from sunlight in late fall and winter. 

What foods give us vitamin D?

Few foods are naturally good sources of vitamin D. The best food sources for vitamin D are fatty fish including salmon, sardines, cod, tuna and halibut. Many foods, such as some breakfast cereals and milk, are fortified with vitamin D. According to federal regulations, milk must contain at least 100 IU of vitamin D per cup. The practice of fortifying milk with vitamin D began in the 1930s to prevent rickets, a bone disease that was common in children at the time. Other dairy products such as yogurt and cheese are not required to be fortified. Milk substitutes such as soy milk, rice milk and nondairy creamer may or may not have added vitamin D.

Natural and fortified vitamin D sources

Food

Serving

Amount IU

Cod liver oil

1 tablespoon

1,360

Cooked mackerel

3.5 ounces

345

Cooked salmon

3.5 ounces

360

Sardines (oil drained)

1-3/4 ounces

250

Tuna (oil drained)

3 ounces

200

Fortified milk

1 cup

100

Egg

1 whole

20

 

Why do we need vitamin D?

Vitamin D is responsible for:

  • Building and maintaining strong bones
  • Keeping the right level of calcium in the blood
  • Keeping the right level of phosphorus in the blood
  • Preventing bones from becoming weak or malformed
  • Preventing rickets in children and osteomalacia in adults

In addition to maintaining healthy bones, recent research on vitamin D reveals it also helps maintain a healthy immune system and may protect against heart disease and cancer, including colon cancer and breast cancer.

The dose of vitamin D currently recommended to maintain a healthy level for the general population is:

Adequate intake per dayAge

5 mcg (200 IU) 

 

birth to 50

10 mcg (400 IU) 

 

50 to 71

15 mcg (600 IU)

 

70+

Doctors are finding that many people now have low vitamin D levels. This may be due to people wearing sunscreen during sun exposure or simply staying inside. But because vitamin D deficiency seems to be more prevalent, researchers are evaluating the current recommended dose and may increase vitamin D requirements in the future.

Too much vitamin D can be toxic. The recommended maximum intake is 25 mcg (1,000 IU) for infants and 50 mcg (2,000 IU) for children and adults with normal kidney function.

Many forms of vitamin D

Most people are not aware that there are many forms of vitamin D. When we eat plant sources of vitamin D, it is in the form of vitamin D2 or ergocalciferol. When we eat animal sources of vitamin D, it is in the form of vitamin D3 or cholecalciferol.

Vitamin D from sunlight, plant sources and animal sources are all turned into 25-vitamin D in the liver. 25-vitamin D is then carried from the liver to the kidneys where it is activated to 1,25-dihydroxyvitamin D or calciferol.

People with chronic kidney disease may get enough vitamin D from the sun and what they eat; however, about half of all chronic kidney disease patients who are not on dialysis and almost all of those on dialysis are not able to activate vitamin D into its usable form of 1,25-dihydroxyvitamin D. As kidney disease progresses, the ability to activate vitamin D to the active form, calciferol, is lessened.

Vitamin D supplements and kidney patients

It is not unusual for people with chronic kidney failure to have low levels of vitamin D. Your doctor may check your vitamin D level and if it is low, order a supplement. The amount prescribed to rebuild vitamin D levels may sound like an enormous amount — a typical dose is 50,000 IU ergocalciferol (vitamin D2) once a week for 6 to 12 weeks. Very large doses such as this are needed to rebuild stores of vitamin D when there is a deficiency. Keeping vitamin D stores in a normal range requires a lower dose of a supplement. Your doctor can best advise you if a supplement is a good choice for you and will tell you if you need it. Always check with your physician before starting an over-the-counter vitamin, mineral, diet supplement or medicine. These items may be harmful to people with chronic kidney disease if not taken properly.

The vitamin D, calcium, phosphorus and parathyroid hormone (PTH) connection

Healthy kidneys are rich with vitamin D receptors and play a major role in turning vitamin D into its active form, 1,25-dihydroxyvitamin D or calciferol. When vitamin D is in its active form, it helps balance calcium and phosphorus in your body by controlling absorption of calcium and phosphorus from the food you eat and regulates parathyroid hormone (PTH). 

When kidneys fail, their ability to activate vitamin D is lost. Without the activated vitamin D to control calcium and phosphorus levels in the blood, parathyroid hormone (PTH) will try to over compensate and go out of range.

Parathyroid hormone (PTH) is secreted by the parathyroid glands that are located in the neck near the thyroid glands. In kidney failure, the parathyroid glands may incorrectly sense that there is not enough calcium in the blood and produce excess parathyroid hormone which tells the body to pull calcium out of the bones and put it in the bloodstream. This excess of parathyroid hormone (PTH) can cause secondary hyperparathyroidism which can result in bone pain and weak bones that fracture easily. All patients with kidney failure are at risk for secondary hyperparathyroidism. For this reason, PTH levels are routinely monitored through lab work approximately every three months or more often if needed.

There are significant problems that may result with excess calcium in the blood stream. Calcium can deposit in soft tissues leaving “little rocks” in the tissue. These deposits or calcifications will never go away. The consequences of calcification are serious. If the heart becomes calcified, blood flow may be reduced, which could cause a heart attack. Calcification in the lungs can result in difficulty breathing. And, calcification in joints can cause extreme pain. 

Vitamin D medicines for dialysis patients

When a person with chronic kidney disease develops a high PTH, a physician may prescribe activated vitamin D to suppress parathyroid hormone production. Hemodialysis patients will be given a prescription medicine intravenously during their dialysis treatment.

Those not on dialysis or on peritoneal dialysis will be prescribed an oral form of activated vitamin D or generic calcitriol. Parathyroid hormone levels are checked regularly to make sure the dose of the medicine is correct and that PTH is adequately suppressed but not over-suppressed. It’s a fine line that the doctor, nurse and dietitian are monitoring.

If a person has a high blood level of phosphorus or calcium, the physician will often choose not to treat the high PTH with activated vitamin D because there is an increased risk of calcium-phosphorus deposits in the soft tissues. It is important for all kidney failure patients to keep phosphorus and calcium blood levels within a normal range. A renal dietitian regularly works with people on dialysis to ensure that they are not eating too many foods rich in phosphorus or calcium and to make sure phosphorus binders are taken correctly.

Summary

The sunshine vitamin plays an important role in the health of people with chronic kidney disease. Vitamin D needs to be activated in the kidney; however, people with kidney failure are no longer able to convert vitamin D to its active form. There are vitamin D supplements available for people with kidney disease who are not on dialysis and medicines for people on dialysis to give them vitamin D. Vitamin D regulates calcium and phosphorus in the blood and without enough vitamin D, the parathyroid hormone will signal the body to take calcium out of the bones, which can be harmful to people on dialysis.

External links


View All Articles in Diet Basics


Have no fear, Diet Helper is here

Download a Cookbook

Get a free recipe collection from the DaVita® kitchen.

No-Cost Kidney Health Classes

Find a no-cost, in-person class near you.

Find a Dialysis Center

Over 2,000 across the US.

Advanced Search

Or call 1-800-424-6589 now to speak with a placement specialist.

DaVita

© 2004-2014 DaVita HealthCare Partners Inc. All rights reserved. Terms of Use | Privacy of medical information | Web Privacy Policy | Safe Harbor Privacy | FAQs | Site map | Advertise with us
This site is for informational purposes only and is not intended to be a substitute for medical advice from a physician.
Please check with a physician if you need a diagnosis and/or for treatments as well as information regarding your specific condition. If you are experiencing urgent medical conditions, call 9-1-1

117