My doctors and I test blood levels of vitamin D on everyone we see in our clinic. When the results come in, two things happen:
1. Pretty much everyone is low in vitamin D.
2. Pretty much everyone is shocked that they are low in vitamin D.
Why worry about vitamin D?
It's important. Multiple studies have shown that people with low levels of Vitamin D have the following:
• Weaker bones 
• Higher mortality rate 
• More allergies and asthma 
• Greater risk of cancer 
• Higher risk of diabetes 
• Greater risk of heart attacks 
• Higher rates of MS 
• Higher risk of infections 
• More mental illness 
• Greater risk for chronic pain 
How much vitamin D do you need?
People absorb vitamin D differently. Because of this, we base having enough on blood levels rather than the dose you would get from pills or foods. The Vitamin D Council argues that 40-80 ng/ml is the amount in the blood that causes the lowest rates of the most diseases. 
What are the most typical vitamin D blood levels?
A study of 18,883 people between the years 2001 and 2004 showed that the average level was 30 ng/ml.  This level is low enough to be categorized as deficient and raise all the risks listed above. This is a big deal and it involves the majority of people.
You may doubt that you could be low in vitamin D because you:
• Already take a multivitamin
• Eat organic foods
• Were prescribed a high dose of synthetic vitamin by another doctor
• Spend lots of time outdoors
Don't multivitamins have enough?
The average amount of vitamin D in multivitamins is 400 IU. This increases blood levels by an average of 4 ng/ml. Unfortunately this is not enough to be helpful. 
Don't we get enough in our diets?
American adults average between 144-288 IU daily from foods.  This is enough to raise blood levels by 2 ng/ml. This is not nearly enough to help. My observation is those who drink lots of full-fat milk fortified with synthetic vitamin D may have enough but they also have other problems like weight gain, poor digestion, and chronic congestion.
What about being in the sun?
Since your body can form vitamin D from sunlight, you would think that spending time outdoors would give you enough vitamin D. People come to expect this even more so here in the Sonoran Desert with well over 300 days of intense sunlight each year.
The problem is that cloud cover, time of day, smog, skin color, clothing, and sunscreen all can change your skin's production of vitamin D. We also don't know if the increased risk of melanoma would be worth the extra sun exposure needed.  Surprisingly, whether you live in northern Canada or southern Mexico it seems to have no bearing on vitamin D from sun exposure. 
One study looked at vitamin D levels of Hawaiian surfers who averaged 15 hours per week in the sun over the last three months. Their Vitamin D levels were as low as 11 ng/ml, which is severely deficient.  Findings like this have led some to speculate that water sports, bathing, and showering, may make our skin less able to absorb Vitamin D.
Besides diet and sun, why else can vitamin D be low?
If all that is not enough, your body fat could be stealing your Vitamin D. It is stored in adipose tissue, also known as fat. The more adipose tissue someone has around his or her waist, the less usable vitamin D they tend to have in their blood. 
How much vitamin D do I need to take to get to a sufficient level?
For most adults, 2000 IU of Vitamin D will raise their blood levels to 20 ng/ml. Therefore, most need 5000 IU of vitamin D daily to reach a blood level of 50 ng/ml. 
What type of vitamin D works best?
Vitamin D3 taken daily is the preferred form. It is best absorbed taken with a meal that has at least 1 small serving of fat from foods like seeds, nuts, oils, avocados, meat, fish, or butter. D3 is widely available in tablets, capsules, and liquids. When taken with food in doses that are high enough, it can absorb well in any form for most people. I do not prefer liquids because it can be difficult to accurately measure the dose each day.
Can you take too much vitamin D?
Yes, but toxicity is not a concern for most. A 2006 study showed that adults who took 100,000 IU of vitamin D daily for 4-6 months showed no signs of acute toxicity.  Blood levels of vitamin D over 150 ng/ml are considered toxic  but I see no reason to be over 80 ng/ml for any length of time.
What should you do?
1. Test your vitamin D level. The name of the preferred test is 25(OH) vitamin D. It can be done by all commercial testing labs with a doctor's order or through home tests commercially available online.
2. Take enough vitamin D3 to reach the Vitamin D Council's recommended range of 40-80 ng/ml. For most people this will range from 4000 IU to 10,000 IU daily. Some people may need higher or lower doses. As always, check with your doctor.
3. Make peace with calcium. Vitamin D will cause you to absorb more calcium. This can be good or bad. Learn more about calcium HERE.
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