By now you’ve heard that your body needs vitamin D to be at its best. Feel free to read HERE to learn more about its many benefits, like lowering risks of:
There has been plenty of focus on the dangers of getting too little vitamin D, but did you know you can also get too much?
By getting “too much”, I don’t mean a toxic overdose. That is possible, but it’s pretty unlikely. Most people would need over 50,000 IU per day for four or more weeks to reach toxic blood levels of over 150 ng/ml.
The concern about getting too much is there seems to be a sweet spot where vitamin D helps the most. If you’re slightly above this sweet spot, vitamin D is not dangerous, but is less helpful.
So, what is the best blood level of vitamin D? Here is what some experts and public figures say:
Wow, this is quite a range! I wish these recommendations lined up, but they don’t. Let’s say you want to think of 30 as the bottom of the best range. Well, the Vitamin D Council says you’re getting too little. If you say 40, then Consumer Lab says you’re getting too much. What’s the upper limit? You can see how there is no amount that will satisfy everyone.
Let’s start with something easy: How little is not enough?
Vitamin D deficiency = <20 ng/ml (40 nmol/L)
Everyone agrees it’s bad to be below 20 ng/ml. At this range, vitamin D is inadequate for bone health and disease risk in general. Past this, we have to start thinking it through and looking at studies.
Types of Vitamin D Studies
The majority of studies used in determining ideal vitamin D levels have looked at people who already have a disease and checked their vitamin D status. These are called, “case control studies”. A smaller number of studies have monitored those with a disease and followed how well they did over time compared to their vitamin D status. These are called, “cohort studies”.
Studies generally look for a relationship between vitamin D and some facet of health. A difficulty is it’s possible to see one facet of health get better while another gets worse. An example would be the medications that lower cholesterol, yet don’t lower the risk of heart attacks.
Mortality Cohort Studies
Because of these concerns, some of the most meaningful studies are those that categorize people based on their vitamin D levels, and watch how long they live.
Most mortality studies on vitamin D show that both too little and too much is bad. Researchers call this a “J-shaped curve”.
Where does the “J” come from? In the image below, the orange line is the J shape. As it shows people too lean on the left of the scale, more die. On the right side, as people get too heavy, more also die.
Note these exact numbers are for illustrative purposes only.
You want to be in the bottom of the J-shaped curve—that’s the sweet spot with the least risk of death.
Nutrients and hormones are normally found in the human body. When we compare how they work in the body with how much we have, a common trend emerges. When the substance is too low, something doesn’t work. As the levels improve, the function gets better, to a point. As the levels get higher, it eventually becomes too much, and things start to get worse again.
We see the same thing for nearly all nutrients studied. If you have too little iodine, your thyroid can slow down. Too much iodine can also slow your thyroid. If you have no vitamin C, you can get a disease, called scurvy. If you take a mega dose of vitamin C and then reduce it, you can get rebound scurvy. Too much testosterone can give a man feminization symptoms, like breast growth. Too little vitamin B6 can cause nerve damage. Guess what overdosing on B6 does? Yes, it causes nerve damage.
What is the sweet spot for Vitamin D and longevity?
The largest single study to date focused on cardiovascular deaths, primarily heart attack and stroke. In it, 247,574 people were monitored for seven years. The population was tracked for vitamin D levels, and these were compared to cardiovascular death.
Results showed death risks were highest for both those lowest and those highest in vitamin D. The lowest risk of death was found in those with vitamin D levels of 30-49 ng/ml, based on the author’s conclusions. 
A large review of several other studies on vitamin D and mortality came to similar conclusions. In it, researchers combined studies, totaling 62,548 people, who were studied for death risk and vitamin D levels. The image below summarizes these studies.
The researchers concluded that those whose vitamin D levels were in the 30-50 ng/ml range had the lowest risk of death.
Another study of all-cause mortality among 13,331 Americans, tracked for 12 years, showed similar results.
A final study of 15,099 American adults, tracked for over 18 years, revealed the same thing: Those with vitamin D in the range of 30-49 ng/ml had the lowest rate of total mortality. 
One last point about the lower limit. A recent study showed that cancer risks among women dropped by 67% in those whose Vitamin D levels were at or slightly above 40 ng/mL.
The study tracked over 3500 women for over 3 years. The average age was 64 and 94% were non-smokers.