With all of the new research on the associations of vitamin D and so many processes and diseases, health organizations and researchers around the globe are exploring the possibility that a majority of the population may be suffering from vitamin D insufficiency if not deficiency.
Note: this is part 2 on a series about vitamin D. Part 1 can be found here.
What is a vitamin D deficiency or insufficiency?
This is somewhat up for debate because those who make these recommendations, such as the Institute of Medicine (a branch of the National Academy of Sciences) and others, feel that only vitamin D’s effect on bone and muscle strength has been proven enough to establish the levels of vitamin D necessary for health. They believe the other health effects have not yet been studied in enough depth to use in establishing recommended levels for optimum health. However, over the past decade many of these organizations have raised their recommendations even when discussing bone and muscle health.
Vitamin D levels are estimated through a blood test which measures the blood levels of 25-hydroxyvitamin D, also referred to as 25(OH)D – an intermediate product between the inactive vitamin D (cholecalciferol) produced in our skin (or ingested as supplements) and the active form of vitamin D (calcitriol).
Currently the Institute of Medicine’s has defined vitamin D deficiency as blood levels of 25(OH)D below 20 ng/ml (50 nmol/l) and insufficiency below 30 ng/ml (75 nmol/l) with more than 30 ng/ml (75 nmol/l) being adequate for health. Some researchers are now calling for raising the level needed for good health to greater than 40 ng/ml (100 nmol/l) and others to even higher. If you don’t understand the units, don’t worry about it. Just know that if you have this blood test in the US the units will probably be the ng/ml. In Europe the units will most likely be nmol/l. But for those who are curious: “ng/ml” is nanograms per milliliter, “nmol/l” is nanomoles per liter.
Vitamin D deficiency/insufficiency may be widespread
Some researchers estimate that at least 50% of the world population are not getting enough vitamin D to ensure healthy bones, an estimate that is backed up by many studies:
- A Canadian study of 577 men and 1,335 women over the age of 35 found approximately 75% with blood levels of 25(OH)D less than 30 ng/ml (75 nmol/l) in the winter and spring.
- A study of 760 schoolchildren in New Dehli, India found more than 84% of the children with blood levels of 25(OH)D less than 20 ng/ml
- In a study of 307 adolescents in Boston, 50% had levels below 25 ng/ml in the summer and almost 75% below 25 ng/ml in the winter.
- In a study of infants and toddlers (age 8-24 months) in Boston, 40% had levels below 30 ng/ml.
- In a large study of 11,247 Australians, 31% had levels below 20 ng/ml (50 nmol/l) and 73% were below 30 ng/ml (75 nmol/l)
- In a large UK study, more than 45% of white adults had levels less than 16 ng/ml (40 nmol/l) while another study showed 33% Asian adults living in the UK may have levels less than 10 ng/ml (25 nmol/l).
I could go on and on with more studies, but I think you are probably getting the picture. Do you know what your vitamin D levels are? At the end of the winter I had mine checked. My 25(OH)D levels were 24 ng/ml! My doctor simply looked at me and said, “You know that is low.” (She knows about my nutrition research). I confessed to purposefully not taking vitamin D supplements for the previous 3 months because I wanted to know what my levels would be without the supplements. Call it a sacrifice in the interest of science. :)
Why are vitamin D levels so low?
The main reason for low vitamin D levels is simply a lack of exposing our skin to the sun for an adequate amount of time when the UVB (ultraviolet B) rays can do their work. There are lots of variables in this simple solution. The darker a person’s skin is the more sunlight it takes to produce vitamin D. The further away a person lives from the equator, the fewer UVB rays make it to earth, therefore, the longer that person must spend outside to make healthy stores of vitamin D. The sun is not as strong in winter and in many places it is impossible to produce much, if any, vitamin D during six months of the year. A dark-skinned person in the far northern or southern latitudes has a very difficult time producing enough vitamin D to maintain health.
Fear of skin cancer has caused many people to cover themselves with sunscreen before venturing outside. This lack of balance in our approach to sun exposure is probably the largest reason for the increase in deficiency. Couple that with the increase in lives spent working inside during daylight hours and then relaxing in our climate-controlled homes and you have a recipe for disaster.
Other reasons for being insufficient in vitamin D stores are: low amounts of vitamin D in the diet, digestive problems which reduce the ability to absorb vitamin D from the diet, and liver or kidney disease. These should all be examined if you suspect vitamin D deficiency.
Ways to increase vitamin D levels
Get out in the sun. How much sun exposure is enough? This is difficult to answer. Some people require only 10-15 minutes several days a week. Some require 2 or 3 hours. It all depends on where you live, what time of year it is, and what your skin type is. A rule of thumb is to stop before your skin starts to turn pink or sting to avoid damaging your skin by overdoing it. Longer is NOT better. There is a limited amount of vitamin D your skin will make in a day – beyond that point you are needlessly exposing your skin to damaging rays.
Increase your intake of foods that are rich in vitamin D. The problem here is that there are very few foods that are rich in this vitamin. The richest sources of vitamin D are fish like wild Pacific salmon, tuna, and sardines, sun-dried shiitake mushrooms (apparently they make vitamin D while drying in the sun), cod liver oil, and egg yolks. In the US some dairy foods, orange juices, and cereals are fortified with vitamin D. However, it is very difficult to get enough vitamin D through your diet. You either must supplement with vitamin D pills or get out in the sun. My opinion is that supplements should be a last resort – but that is an topic for another post.
Recommended amounts of D3
Now this is a sticky issue. If you get plenty of unblocked sunshine during the summer and the winters aren’t too long where you live, you might not have to worry about how much vitamin D to consume or take. By getting your levels up high enough during the summer, you might be able to go several months in the winter without your levels dropping to dangerous levels. The plus to making it naturally is that it appears to be impossible to get too much vitamin D this way. The human body is designed to stop making it when there is enough.
The recommended intake of vitamin D used to be 400 IU of vitamin D3 per day (note: vitamin D2 is not as potent), but many sources are now recommending a minimum of 1000 IU each day with a few recommending even more. For a reference point: a serving of salmon may give you 360 IU and an egg yolk provides 20 IU. Most sources seem to believe a person can take up to 4000 IU safely. When I first saw how low my 25(OH)D levels were I started off taking 2000 – 4000 IU per day. I have since switched to trying to manufacture it naturally in the sun.
Do you have any questions about vitamin D? Post them in the comment section and I will try to research the answer.