Vitamin D: A Key To Endurance Sports Performance

What You Can Do

– Check 25(OH)D levels regularly and supplement as needed.
– Check for total 25(OH)D and not 1, 25(OH)D, which will tell you nothing about your blood stores. Total 25(OH)D reflects all sources of Vitamin D – from food, UV energy (photo-production), and supplementation.
– Deficient athletes measuring less than 30 ng/ml should supplement with 20,000 IU to 50, 000 IU of vitamin D3 per week for eight weeks andrecheck serum 25(OH)D until normal values are attained.
– Get regular, safe, twice-daily (5-30 minutes) exposure to sun between the hours of 10 am and 3 pm. Note that sunscreen and glass (being indoors) reduce or block UV energy.
– Supplement with 1000 IU to 2000 IU of Vitamin D3 to maintain normal levels.
– For those living or competing in northern latitudes (north of Atlanta) little to no vitamin D production will occur, so consumption of fortified foods and supplements is a necessity.

Food Sources of vitamin D

There aren’t many naturally occurring foods that contain vitamin D. Most of the foods containing Vitamin D have been fortified, for example milk and certain juices.

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Table 1. Food Sources of Vitamin D

FOOD Serving IU per serving *
Fish liver oils (cod liver oil) 1TBSP 1360
Herring, cooked 3 oz 1383
Wild salmon, cooked 3.5 oz 981
Farm salmon, cooked 3.5 oz 249
Tuna, canned in oil 3.5 oz 200
Milk, non fat, reduced fat, whole (fortified) 8 oz 100
Margarine, fortified 1 TBSP 60
Egg 1 whole 18
Beef, liver 3.5 oz 15
Cheese 1 oz 12
*IU = International Units

Dietary Supplement Fact Sheet. National Institute of Health (2007)


High intakes of Vitamin D can cause nausea, vomiting, poor appetite, weakness, and constipation. Current safe upper limits are set at 2,000 IU by the National Institute of Health, but there are newer data supporting upper limits as high as 10,000 IU per day.


About The Author:

Reyana Ewing, MPH, RD, CLE is a registered dietitian, sports dietitian and runner based in Santa Rosa, Calif. Find our more about her at

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