Even though DDT has not been used for decades, most people have a low level of DDT in their bodies. It appears that all organochlorine pesticides, not just DDT decrease the vitamin D blood levels The more the pesticide, the less the vitamin D. Most Americans have less than 20nanograms/gram of DDT in their blood. It "appears" that 20ng/g level of DDT decreases the vitamin D level by 3-4ng/ml

Links for more information

• All of the reasons for vitamin D deficiency
• DDT and other pesticides decrease vitamin D – Jan 2012
• Extremely long list of organochlorine pesticides