In 2010, the Institute of Medicine established that a blood level of 20 ng/ml of vitamin D was enough for 97% of the population. A recent study from Johns Hopkins University adds that taking vitamin D supplements for most does not provide any benefit. It can actually be harmful (cardiovascular and kidney diseases) and is nothing more than a waste of money. However, they suggest that people with kidney diseases and other medical conditions could benefit from vitamin D supplements, a recommendation also supported by the Mayo Clinic.
There are however conflicting opinions on the subject on vitamin D requirements. Many doctors believe that a value below 30 is unhealthy. The 30 ng/ml value is the previous standard set by the IMO (adjusted to 20 ng/ml in 2010). That value made most American children and adults deficient in vitamin D, whereas the current standard (20) makes most in the acceptable range. An organization called the Vitamin D Council even suggests that levels below 40 are deficient (making almost everybody deficient), despite the fact that the Institute of Medicine warns that levels above 50 are dangerous. Another study showed that levels below 20 ng/ml had adverse effect on people with kidney diseases.
What’s more, a research conducted by Kaiser Permanent recently showed that vitamin D supplements actually contain between 9% and 146% of the vitamin D they claim to provide. So no one knows how much vitamin D they actually consume by taking supplements.
According to many physicians, the best source of vitamin is from the sun. Exposing arms and legs, without sunblock but before 10:00 am and after 4:00 pm, a few hours a week provide enough vitamin D. They also suggest to get tested by your doctor and increase sun exposure if you are belong 20 ng/ml, as sun exposure has the greatest impact on vitamin D levels (far more that food for instance)
Also, avoid meat and dairy as studies have shown that consuming animal protein reduces the amount of vitamin D in the body.