Here are some studies where scientists are trying to figure out what the best vitamin D doses are:

Diagnosis and Treatment of Vitamin D Deficiency (2008)

Note: Incredibly comprehensive article from world-renowned vitamin D experts Dr. John Cannell and Dr. Bruce Hollis covering optimal vitamin D dosing.

 

Use of Vitamin D in Clinical Practice (2008)

Note: Another incredibly comprehensive article from world-renowned vitamin D experts Dr. John Cannell and Dr. Bruce Hollis covering how to maintain adequate vitamin D levels.

 

Human Serum 25-Hydroxycholecalciferol Response to Extended Oral Dosing with Cholecalciferol (2003)

Conclusion: 67 men living at a high northern latitude were given a daily dose of either a placebo, 1000 IU vitamin D3, 5000 IU vitamin D3, or 10,000 IU vitamin D3 to take daily throughout winter. By the end of the study, five months later, only the men taking 5,000 IU and 10,000 IU had achieved vitamin D levels in the adequate range, with the 10,000 IU group having the most optimal levels. Those taking 1,000 IU daily achieved vitamin D levels only just slightly higher than the placebo group. All groups had an almost identical starting vitamin D level. These researchers concluded that taking 10,000 IU daily was completely safe for these men and none of them developed elevated calcium levels and the highest vitamin D level achieved by any of the men was still within what is considered the safe,healthy range. Optimal vitamin D dosing requires amounts higher than historically recommended by doctors.

 

Vitamin D Supplementation, 25-Hydroxyvitamin D Concentrations, and Safety (1999)

Conclusion: This is a meta-analysis of many studies investigating the effects of different vitamin D doses on their vitamin D level-raising effects. These researchers conclude that the average adult needs at least 4,000 IU of vitamin D daily – far more than is typically recommended. However, these researchers state that the 4,000 IU daily is to ensure a vitamin D blood level of 40 ng/ml, but since this study vitamin D experts have concluded that 50 ng/ml is actually the minimum level everyone should maintain. So the daily dose the average person needs is actually higher than 4,000 IU. Even 10,000 IU daily has been found to be safe for adults and keeps people well below the potentially toxic level. Of course, this all depends on your own body weight/size, amount of body fat, skin type, sun exposure, current vitamin D level, and calcium intake.

 

Vitamin D and Its Major Metabolites: Serum Levels After Graded Oral Dosing in Healthy Men (1998)

Note: This is just an interesting study that tested the vitamin D level-raising effects of many different dose sizes of multiple forms of vitamin D on adult men. Predictably, giant doses (50,000IU/daily for two months) are too much and push levels beyond the toxic range, but the typically-recommended doses of 400 IU and 800 IU are not enough.

 

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