Vitamin D Basics

There has been much ado in the media in recent years on the benefits of both a diet high in vitamin D or supplements. Is it good” Is it bad? Does it work? Vitamin D’s most recognized role in the body is for bone health. It has been shown to help to increase absorption of calcium, which in turn helps maintain strong bones.

More recently, research on vitamin D has been linked to immunity, anemia, mental health and heart health. Studies in chronic kidney disease (CKD) have been focusing on anemia management and the effects of hyperparathyroidism. This post will explain some of the basics within the guidelines of vitamin D management in CKD.

Laboratory

According to the Institute of Medicine and the Kidney Disease Outcomes Quality Initiative (KDOQI), the best test for vitamin D is serum (blood) 25-hydroxyvitamin D3 (serum25(OH)D3). The optimal level for people with CKD has been suggested at 30-40ng/mL but there are no standard guides right now because of a lack of research. You should ask your primary care doctor to check your levels once a year. Doctors can then suggest how much vitamin D you may need.

Vitamin D in food and supplements

There are a few different forms of vitamin D. Nutritional vitamin D is found in fatty fish like, salmon, mackerel, and tuna; also in eggs, cod liver oil, mushrooms and fortified breads, cereals, milk and orange juice. (ODS NIH fact sheet) The amount of vitamin D found in many of these foods is known to be very small (<200 IU per serving), and as kidney function declines, it is very difficult to eat enough vitamin D to maintain optimal levels.

Supplemental oral vitamin D may come in small or large doses and two types, D2 (Ergocalciferol) and D3 (Cholecalciferol). D2 is made from a yeast ergosterol when exposed to light and is often added to breads and cereals as “fortification”. D3 is the natural form synthesized in the skin by UVB radiation or found in fatty fish. It may look like a gel cap or a white powder capsule. Both of these supplements are inactive, meaning they need to be processed by the liver and the kidneys before they can be active in the body. In cases where kidney or liver function is impaired, a doctor may prescribe calcitriol. This is the active form of vitamin D which is made in the kidneys.

How much do I need?

If your blood levels of 25(OH)D are greater than 30 ng/mL you may be getting enough vitamin D through food. The recommended daily allowance is currently 600 IU for children and adults up to age 50 years and 800 IU per day for over age 50 years. This can be difficult since vitamin D is found in very few foods, and you may have to eat a lot of these foods to get enough vitamin D every day!

For example you may need a 3 oz. of salmon (1 serving) and 2 servings of dairy a day OR 9 oz. of tuna (3 servings), 2 servings of dairy a day. But, you can also simply spend 15 minutes a day outdoors with face and arms exposed to sun (without sunscreen). You should always first consult your dietitian and your doctor.

If your levels are low, less than 20 ng/mL, supplementation of higher doses may be recommended by your doctor. Clinical trials of doses of 50,000 IU weekly for four weeks followed by routine supplementation were effective in raising levels of vitamin D to 30-40 ng/mL. Although these recommendations are from the KDOQI guidelines, you should always consult your doctor or a dietitian before taking a vitamin D supplement in order to get the best plan for your body.

Summary

In summary, you should always consult your doctor and/or dietitian before starting any supplement. Best practice is to have your 25-hydroxyvitamin D measured once a year by your primary care doctor. If your levels of 25-hydroxyvitamin D are normal you may be getting enough through either food or sunshine. When levels are low, there are several forms of supplementation available over the counter or by prescription. These include the inactive form of vitamin D, cholecalciferol or ergocalciferol; or the active form of D, calcitriol. Your doctor or dietitian can help determine the proper dose needed. They can also monitor your vitamin D levels and adjust supplement dose as needed.

Click here for additional kidney diet tools and resources from DaVita.

References

1. NIH ODS Factsheet:  https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
2. Holick MF. J Clin Endocrinol Metab.2011;doi:10.1210/jc.2011-0385
3. Kumar, V K et al. Vitamin D supplementation and recombinant human erythropoetin utilization in vitamin D-deficient hemodialysis patients. Jnephrol 2011; 24 (01): 98-105
4. National Kidney Foundation. K/DOQI Clinical Practice Guidelines for Chronic Kidney
5. Disease: Evaluation, Classification and Stratification. Am J Kidney Dis 39:S1-S266, 2002 (suppl 1)
6. Stauffer ME, Fan T (2014) Prevalence of Anemia in Chronic Kidney Disease in the United States. PLoS ONE 9(1): e84943. doi:10.1371/journal.pone.0084943

This article is for informational purposes only and is not a substitute for medical advice or treatment. Consult your physician and dietitian regarding your specific diagnosis, treatment, diet and health questions.