Yet another study (Feb 2012) has shown weight loss when taking vitamin D.
Many studies in the past few years have shown that some fraction of obese women lose weight when taking vitamin D - without going on any diet
Overview Obesity and Vitamin D has scores of references to vitamin D and Calcium for weight loss and had the following summary March 2012
- FACT: People who are obese have less vitamin D in their blood
- FACT: People who are obese need a higher dose of vitamin D to get to the same level of vitamin D in their blood
- FACT: When obese people lose weight the vitamin D level in their blood increases
- FACT: Adding Calcium, perhaps in the form of fortified milk, often reduces weight
- OBSERVATION: About 30% of obese quickly lose weight when they take >2000 IU of vitamin D and 750 mg Calcium
   Women lose weight, men have not been tested
- SUGGESTION: Probably need much more than 2,000 IU to lose weight if very low on vitamin D (high risk) due to
  risk factors such as age, dark skin, very overweight, live far from equator, etc.

There has been lots of speculation as to why vitamin D reduces weight in some obese women

Vitamin D ==> reduce pain ==> get up and about ==> reduce weight paraphrased from the Vitamin D Council
Weight reduction review – Vitamin D and Calcium may help has the following chart
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Summary by Vitamin D Life for obese women (no data about men) who are overweight/obese

Try taking enough vitamin D for several months to see if you are the 1 in 3 women who can lose weight with vitamin D
There is extremely little risk and cost in your seeing if vitamin D acts as a diet pill for you.
To learn how much to take, click on the references above. (range: 1,000 to 15,000 IU per day)