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