Yes and no. It depends on what levels are deemed most healthy, which unfortunately is not agreed upon among researches and experts. There are currently two opposing views that truly boils down to a case of adequate levels versus suggested optimal levels based on strong recent evidence. Although the Institute of Medicine (IOM) recently tripled the Vitamin D recommendation (from 200 IUs to 600 IUs for most adults), they also believe that most Americans blood levels are safely above the 20 ng/ml (nanograms per milliliter) level that is deemed adequate. With the IOM acknowledging research showing that most American diets fall far short of even the old lower recommendation of 200 IUs, they concluded that most people must be making up the dietary shortfall through sunlight and/or supplements. This explains why the answer to this question is “no” - most people do not have blood levels of vitamin D below the adequate level of 20ng/ml because they get to this level from supplements and/or sunshine since it’s obvious that their diet is insufficient.
On the other hand, most top Vitamin D researchers still think both the vitamin D blood level cut off and new dietary recommendations are still too low. Many recent studies have linked significantly higher blood levels of Vitamin D to a reduced risk of many chronic diseases including heart disease, hypertension, cancers, diabetes, infections and falls. Therefore, most Vitamin D experts recommend blood levels of vitamin D (25-hydroxyvitamin D [25OHD]) to be no less than 30 ng/ml. This may require a daily intake of at least 1000 IUs of Vitamin D. The strength of evidence for increased blood levels of vitamin D has lead many physicians to order blood tests for their patients costing between $100 and $200. The blood levels of 25OHD deemed normal by the National Institute of Health (NIH) as posted on their MedlinePlus website is a range between 30 and 74ng/ml. This is where the Vitamin D experts would like to see blood levels since these levels appear to decrease the risk of disease. In order to reach these levels most people would need to supplement the diet since sunshine is not considered a safe or reliable therapy.
This is why the answer to this question is ultimately “yes” - the suggested “better than adequate” blood level would be at least 30ng/ml and most Americans fall short, meaning they should supplement the diet if they want to hedge their bets against certain common diseases.