Vitamin D

After I had my first child, I was convinced that something was wrong with me, I didn’t feel right.  I didn’t have the luxury of a logical brain at the time saying “you are not sleeping and you haven’t sat down to eat in months.”  So, I rushed to the doctor and asked to have my labs checked.  The labs showed my vitamin D level to be 22.  I understood that to be “low” so I vowed to take a vitamin D supplement (which lasted all of 2 weeks).  Then I decided to investigate vitamin D a bit more.  I found lots of articles about Vitamin D.  There is an entire council dedicated to vitamin D -- an “international project to solve the vitamin D deficiency epidemic.” There have been countless headlines spelling out how vitamin D can cure anything from depression to cancer.  Yet, the best evidence we have hasn't supported these headlines. In 2010 the Institute of Medicine stated that average daily requirement for vitamin D is 400 IU.  The primary source of vitamin D is the sun.  The amount of vitamin D we get from the sun is quite variable from person to person.  Absorption is affected by the amount of skin pigmentation (darker skin takes longer to absorb vitamin D), the time of day (high noon has more vitamin D exposure), if sunblock is used (this will decrease absorption) and how much skin is exposed.   This study showed that an individual in Boston from April to Oct at 12pm EST with 25.5% of their skin exposed would need 3-8 minutes in the sun to synthesize 400 IU of vitamin D.  So, it doesn’t take very long to get the daily requirement. However, for many of us who spend a lot of time indoors, or who cover up very well in the sun, it might be a challenge.

There are some food sources of vitamin D but they are not plentiful.  Milk often has vitamin D added to it and is the most common source of vitamin D in the American diet.  Fatty fish skin and livers and egg yolks are other more common sources.  This article has a great table with foods and their vitamin D levels. There is controversy over what is considered an “optimal” serum vitamin D level.  The Institute of Medicine says serum vitamin D levels (measured as 25(OH) vitamin D) should be above 20ng/ml (50nmol/L).  Other organizations (the Endocrine Society, National Osteoporosis Foundation, International Osteoporosis Foundation, American Geriatrics Society) say that the level should be at least 30ng/ml (75nmol/L) for older adults.  Although there are few long-term safety data, the Institute of Medicine defined the Safe Upper Limit for vitamin D consumption as 4000 IU per day.   They also recommended avoiding reaching serum levels of vitamin D of more than 50ng/ml.  This is based on some question of increased mortality when above these levels.

There are many health problems that have been connected with vitamin D, but very little of our best science to vet out the truth.  One issue that has a bit more clarity than others is that for people over 65 years old, taking vitamin D at 800 IU per day may help prevent falls.  (However, tai chi and exercise therapy are more clearly proven to prevent falls.) For a bit more perspective, think of it this way, in general, people who have lower serum levels of vitamin D tend to be people who are obese, institutionalized, have significant intestinal diseases like Crohn’s disease, or are taking medicines which affect vitamin D.  So when we find that people with lower serum vitamin D levels have more cancer, diabetes, and cardiovascular disease, we are not proving that these problems are caused by low vitamin D.  It’s a dangerous leap in assumptions.  Perhaps it’s the obesity causing the diabetes and the vitamin D deficiency.

There are very few randomized trials looking at mortality associated vitamin D supplementation, meaning, not a lot of good science to tell us if taking vitamin D will make us die earlier or later.  When we look at large populations of people (epidemiological studies), and compare their serum vitamin D levels with mortality (likelihood of dying), some studies showed us that people with low levels (<10) of vitamin D had a higher mortality.  But other studies showed no association.  Again, these studies looked at vitamin D levels in the blood, but not at the effect of taking a vitamin D supplement.  It’s akin to the observational studies of beta carotene, showing higher levels meant less cancer, but you know how that one ended (if not, then read my last blog).  We really don’t have the data yet to show how taking a vitamin D supplement affects mortality.

There are a couple of situations where the need for vitamin D supplementation may be important.  One is for newborn infants who are solely breast fed.  Because the breast milk often has low levels of vitamin D and rickets is seen almost always in exclusively breast fed infants (96% of rickets cases).  The American Academy of Pediatrics recommends supplementing with 400 IU of vitamin D daily in infants shortly after birth.  This study shows that vitamin D needs would be met if a baby was in the sun in a diaper alone for 30 minutes per week or fully clothed with a hat in the sun for 2 hours per week.

In osteoporosis, the data shows that vitamin D alone doesn't reduce the risk of fracture unless there is adequate calcium. More to come on calcium supplementation for osteoporosis.

So, based on all of this, if you are over 65 years old, you could think about taking a vitamin D supplement of no more than 800 IU per day (choose vitamin D3), but don’t feel too worried if you miss it.   However, I wouldn’t recommend skipping the exercise.  For those under 65, you can decide for yourself.  For now, I’m going to skip the vitamin D supplement and enjoy a few minutes in the sun now and then.