Vitamin D can be obtained from three sources: food, ultraviolet light (sun and UV lamps), and supplements. Since each person’s vitamin D is affected differently by sunlight, nutrient absorption from food and supplements, and mobilized body stores, there is no one-size-fits-all guideline. Sunlight or UV exposure is the optimal source of vitamin D and accounts for the majority of 25(OH)D serum levels in the absence of supplementation. With the winter months upon us, we have less daylight hours, typically spend less time outdoors, and are usually all bundled up preventing much skin from actually being exposed to the sun. The range of serum 25(OH)D, which the majority of researchers agree, that avoids deficiency or toxicity is between 30 and 60 or 65 ng/mL.
Food Sources of Vitamin D
Food (3.5 oz. unless otherwise specified); IU per serving
High-vitamin cod liver oil (1/2 tsp.) 2,000
Indo-Pacific marlin 1,400
Fatty bluefin tuna 720
Duck egg 720
Chicken egg (pastured) 480–720
Rainbow trout 600
Standard cod liver oil (1 tsp.) 400
Sockeye salmon 360
Canned sardines 270
Chicken egg (conventional) 120
Pork liver 50
Beef liver 13.5
Chicken liver 30
As a general rule, mid-summer full-body skin exposure produces 10,000 IU in about half the time it takes your skin to turn pink. This could be just 15 minutes for pale skin types.
At higher elevations, for darker skin colors, or with less skin exposed, much less vitamin D is produced.
Recommended Sun Exposure by Season
Late fall, winter, and early spring: Spend about half as much time as it takes for skin to turn pink outside three to seven times per week.
Late spring, summer, and early fall: Spend half as much time as it takes for skin to turn pink outside at least three times per week.
Take with fat for maximum absorption.
D3 is better absorbed than D2.
Your dose should be adjusted according to your weight.
Weekly or daily dosing is similarly effective.
Avoid monthly or semi-annual mega-doses.