I am writing this while away in Colorado during the holidays. The snow-covered mountains are truly gorgeous and instill a peace that I needed as the New Year approaches. Although I am not skiing, I watch those who are come down from the mountain. They are covered from head to toe (so am I, to keep warm) and although they are in the sun, most are slathered in sun block. So being the negative thinking doctor that I am, I wonder what their vitamin D levels are? And then as I read the publication “Postgraduate Obstetrics and Gynecology (it’s a biweekly publication for continuing medical education), I came across an article titled “The New Face of Vitamin D”. I’ve written several articles about “D” but I thought the authors summed up the data very well and so I would like to share this year’s “D” facts with you.
Vitamin D has always been considered a bone-necessary vitamin. Without it children developed rickets and adults were likely to lose bone density and risk osteoporotic fracture. “D” is needed to facilitate the absorption of calcium and phosphate from the intestine; and if there is not enough calcium “on board” (hypocalemia), the parathyroid (glands on both sides of the thyroid that regulate calcium) goes into overdrive to get calcium into the circulatory system from the body’s calcium depository (the bones), causing bone demineralization.
We now know that nearly every tissue in our body has Vitamin D receptors; and if they are insufficiently “fed”, the systems that are made up of these tissues can go awry. Here are some of the systems that are affected and disorders that are more likely to occur with inadequate vitamin D:
The Immune System
Vitamin D is an immunosuppressant. That means it may be helpful in protecting us from autoimmune disease in which antibodies attack our cells. A study published in 2006 showed that Vitamin D either helped prevent or reduce the severity of multi[le sclerosis.
Vitamin D may impact glucose metabolism. The Nurse’s Health Study which followed more than 83,000 women fund that those who took at least 800 IU (international units) of Vitamin D has a 33% lower risk of developing type II diabetes. And a study of 10,000 children demonstrated a 50 to 80 % decrease in the risk of type I diabetes in children who received the recommended dose of Vitamin D.
High doses of Vitamin D have been shown in multiple studies to have a protective effect against colon cancer especially in women older than 60. There are ongoing investigations to ascertain whether this holds true for other cancers especially breast cancer.
Low Vitamin D levels have been shown to be associated with a higher rate of heart attack and increased cardiovascular mortality. An ongoing 5-year study of 20,000 subjects (called VITAL, don’t you just love these acronyms that researchers make up…) will help determine if Vitamin D supplementation can help prevent cardiovascular disease.
Women who have the lowest levels of Vitamin D have been shown to have higher rates of preeclampsia compared to those who take Vitamin D. They may also have more vaginal infections with bacteria that don’t like oxygen (anaerobes) and this type of vaginitis has been accepted as a risk factor for preterm birth. Low maternal Vitamin D levels also means low levels in the fetus and (at least in rats) may affect brain development.
An overall review of the literature points to the fact that there is an approximate 26% reduction in hip and nonvertebral fractures in adults with supplementation of 800 IU of Vitamin D daily. This benefit was not seen with supplementation of only 400 IU of Vitamin D daily.
So now that I have given a quick overview, it’s quite clear that we need our “D”… I’ll give you some statistics as to how many of us are D deficient. Let’s start with the number 1 billion. (No, it has nothing to do with our national deficit.) That’s how many people worldwide are thought to be “D” deficient. In the US, depending on the data that is published, 25 to 57 % of us lack enough “D”.. The percentage is generally thought to be higher at 68%. In postmenopausal women its 50%
Our primary source of Vitamin D is the sun. It radiates ultraviolet rays that, when absorbed in our skin, produce pre-vitamin D. This is converted to (sorry think this is a bit scientific) to 25-hydroxyvitamin D in the liver, which then releases it in two forms, Vitamin D3 and Vitamin D2. The majority of “D” is stored in our body as Vitamin D3. Your Vitamin D level can be determined though a blood test that measures total 25- hydroxy D.
Skin can produce 20,00 to 50,000 units of vitamin D with 30 minutes of midday exposure. But most of us inhibit this source of “D” because we use sunscreen, cover our bodies with outdoor clothes, or dress in a way that is deemed socially acceptable. We obviously get less sun exposure in northern latitudes or during winter months. The darker our skin from the pigment melanin, the less we absorb those ray. (This causes Black and other dark skinned individuals to be particularly susceptible to “D” deficiencies.) Obesity will promote sequestering of “D” in fat cells so that the vitamin is not available for the body’s utilization. And finally vitamin D production slows down with age.
Unlike other vitamins it’s hard to get enough “D” though diet. Unless you consume herring (3 oz. have 1383 IU), cod liver oil (1 tablespoon has 1360 IU) or salmon (3 oz. have about 500 IU) your food may not suffice. (Other fish average less than 150 IU for a 3-ounce serving, and 8oz. of fortified cow’s milk has only 120 IU).
Hence, it would seem that most of us should supplement, but how much? Well that remains controversial.. There are many researchers and health organizations that proclaim that as long as our “D” level is above 30 ng/mL or even 40 ng/mL we will achieve the beneficial effects of vitamin D. Levels below 20ng/mL lead to bone density problems so the goal is to stay at least above that. . (My lab considers the above 30 to 100 to be normal range.) The Institute of Medicine (IOM) states that for women age 18 to 70 the daily recommended intake is 400 to 600 IU. For women over 70, it should be 800 IU. They increased the safe upper limit to a range of 2000 to 4000 IU. Having said that, ACOG and other organizations as well as many doctors are considering recommending higher doses. Too much “D” can be toxic, but toxicity has not been found with doses of up to 10,000 IU daily. Moreover since Vitamin D is fat-soluble it can be given daily, weekly or monthly.
I now suggest that my patients get at least 1,000 IU a day. In women who may be high risk for “D” deficiency, I measure their Vitamin D level. If it is low, I might increase their dose or prescribe 50,000 IU of vitamin D to be taken by mouth weekly for 12 weeks and then retest their level. I, personally, take 2,000 IU of vitamin D a day…to hedge my bets. No, I did not stand at the bottom of the ski run and proffer “D” supplements to the skiers.