What causes a vitamin D deficiency?

There are many possible causes of vitamin D deficiency.

Limited exposure to the sun

You may look out your window and see the sun shining and think that you are safe from this deficiency, but that is not always the case. Even in sunny climates there is an increased prevalence of vitamin D deficiency.

We have all heard about the dangers of skin cancer and the need for sunscreen to protect us from this disease. This knowledge and the preventive actions we take have significantly decreased our vitamin D levels. Sunscreen protects so well against UV-B rays that an SPF of 30 decreases vitamin D synthesis in the skin by more than 95%. On top of this, we tend to spend more time indoors. One study found that it took Caucasians exposure of more than 30% of their body every day in the summer to make the optimal amounts of vitamin D. Most adults work indoors and wear more clothing during the work week, which leaves only about 10%-15% of their body exposed to UV for short periods, so they cannot meet their vitamin D needs through the sun alone. Even if you do have some exposure to the sun, the total amount of vitamin D you can produce is affected by the season, time of day, ozone amount, latitude, and number of clouds in the sky. The important thing about using the sun for vitamin D production is to know that less is more. You are better off with short regular exposures to the sun rather than prolonged exposure for many reasons. The process is not as simple as the sun hitting your skin and vitamin D appearing in your blood. What actually happens is that vitamin D3 is first transformed by a process known as hydroxylation in the liver to 25-hydroxyvitamin D3, often written as (25(OH)D3), and then again in the kidney to its active form, 1,25-dihydroxyvitamin D3, written as (1,25(OH)2D3). The level that is checked in your blood is 25-hydroxyvitamin D, often written as 25(OH)D, which includes vitamin D2 and D3. By staying in the sun, you limit this process and can actually get less vitamin D. You also have a lower risk of burning and damaging your skin with short exposures.

Darker skin

Melanin is what gives skin its color. Lighter skin has less melanin than darker skin. Melanin is able to absorb UV-B radiation from the sun and reduce the skin's capacity to produce vitamin D3 by 95%-99%. People with a naturally dark skin tone have natural sun protection and require at least three to five times longer exposures to make the same amount of vitamin D as a person with a white skin tone. African Americans have a population mean serum 25(OH)D level of 16 ng/mL, whereas white Americans have a level of 26 ng/mL. 

Weight

Being overweight or obese may put you at risk for a vitamin D deficiency. A study done on 2,187 overweight and obese subjects found that those with a BMI above 40 had 18% lower serum vitamin D levels than those with a BMI under 40. Another study compared the vitamin D levels of 154 obese subjects to those of 148 nonobese subjects and found that the obese subjects' vitamin D levels were 23% lower. While diet and decreased sun exposure may have some impact on this, there appears to be an increased need that cannot be met without a supplement. One study tested the blood levels of vitamin D after sun exposure in both obese and nonobese subjects. Both saw an initial rise in vitamin D levels after similar exposures, but 24 hours later, there was 57% less vitamin D in the blood of the obese subjects. Both groups had a similar capacity of the skin to produce the vitamin. The difference was seen in the release of vitamin D from the skin into the circulation. It is believed that the fat under the skin holds onto the fat-soluble vitamin instead of releasing it, but more research needs to be done to confirm this. It is also not clear if weight loss causes an increase in vitamin D levels due to the fat cells releasing it into circulation. Some studies have shown small increases and others have not. Those who are losing weight should discuss the impact this may have on vitamin D levels with their health-care provider. For those who wonder if a vitamin D deficiency can contribute to weight gain, so far one study tested this and did not show this to be the case.

Malabsorption

People with one of the fat malabsorption syndromes (for example,Crohn's disease, celiac disease) and people who have had bariatric surgery are often unable to absorb enough of the fat-soluble vitamin D.

Age

It has been shown that as we age our body has a decreased ability to synthesize vitamin D from exposure to the sun. There can be as much as 25% reduced production over the age of 70. While this can have an impact, it doesn't cause as much of a deficiency as the other risk factors.

Medications and medical conditions

A wide variety of medications, including antifungal medications, anticonvulsants, glucocorticoids, and medications to treat AIDS/HIV can enhance the breakdown of vitamin D and lead to low levels. There is also a loss of vitamin D for those with chronic kidney disease, primaryhyperparathyroidism, chronic granuloma-forming disorders, and some lymphomas

All it takes is a simple blood test to find out if you are deficient in vitamin D, but you need to have the right test done. There are two blood tests for vitamin D. One is 1,25(OH)2D. This is one is not a good measure for your current vitamin D level. It has a short half-life and can be impacted by your parathyroid hormone (PTH), calcium, and phosphorus levels, so it's not a true measure of your vitamin D status. The preferred test is the 25-hydroxyvitamin D, written as 25(OH)D. This is the most accurate measure of your current status as it reflects what you get from your diet, from supplements, and from the sun. It is also the one that the majority of the research studies measures.Again, there are two sets of guidelines written by both the Institute of Medicine (IOM) and the task force for the Endocrine Society. These levels are for serum (blood) 25(OH)D

Vitamin D3 has been shown to be the best choice for supplements. Vitamin D2 supplements do not raise your levels the same amount as D3 and, in some cases, they have been shown to decrease levels over long-term use.

The amount of vitamin D that is needed to correct a deficiency will depend on the severity of the deficiency and your individual health risks. The time of year will also matter. For example, if you are on the low end of adequate blood levels and heading in to the winter months you would need a bit more than if you were heading in to the summer months. The goal for everyone is to get your stores to a safe level and prevent them from dropping with a maintenance plan.

What you take is as important as how you take it. Vitamin D supplements should be taken with a meal that contains fat. Studies have shown that when taken on an empty stomach versus with a meal containing fat, there was an average of 32% more vitamin D absorption in the fat-containing meal. This ranged from 11%-52%. Even an 11% reduction is significant and can impact your vitamin level. A recent study instructed people to take their supplement with their largest meal (typically the one with the most fat), and in three months, their blood levels went up an average of 56.7%.

There are supplements that can be taken on a daily, weekly, or monthly basis. It's a matter of preference and, most importantly, which one you will be more likely to take. You may start out at a higher dose and decrease after a month or two. Most experts feel that the goal is to get your level above 30-40 ng/mL, depending on your risk factors, and then take a maintenance amount. When you are deficient, it is recommended to have your blood tested after two to three months of taking the supplement to be sure that your levels are going up. Work with your doctors to find the optimal plan for you.

The task force for the Endocrine Society makes the following recommendations:

• For children 1-18 years of age who are vitamin D deficient, we suggest treatment with 2,000 IU/d of vitamin D3 for at least six weeks or with 50,000 IU once a week for at least six weeks to achieve a blood level of 25(OH)D above 30 ng/ml, followed by maintenance therapy of 600-1,000 IU/day.
• We suggest that all adults who are vitamin D deficient be treated with 50,000 IU of vitamin D3 once a week for eight weeks or its equivalent of 6,000 IU of vitamin D3 daily to achieve a blood level of 25(OH)D above 30 ng/ml, followed by maintenance therapy of 1,500-2,000 IU/day.
• In obese patients, patients with malabsorption syndromes, and patients on medications affecting vitamin D metabolism, we suggest a higher dose (two to three times higher; at least 6,000-10,000 IU/day) of vitamin D to treat vitamin D deficiency to maintain a 25(OH)D level above 30 ng/ml, followed by maintenance therapy of 3,000-6,000IU/day. One study found that for every 33 lbs. of body weight the serum 25(OH)D level was 4 ng/ML lower at the end of one year of monitoring. This could lead to a significant change in the amount required to supplement based on your body weight and starting serum level.

A few foods naturally contain vitamin D, and other foods are fortified with it. Most people can get at least some of their vitamin D needs from the sun. The amount found in food is not enough for treating a deficiency and may not be enough for most people to maintain adequate levels unless combined with sun exposure. Still, getting it from your diet when possible is a good idea.1 tsp cod liver oil has 400 to 1,000 IU/vitamin D

• • 3.5 oz salmon, fresh (wild) has 600 to 1,000 IU/vitamin D
  • 3.5 oz salmon, fresh (farmed) has 100 to 250 IU/vitamin D
  • 3.5 oz salmon, canned has 300 to 600 IU/vitamin D
  • 3.5 oz sardines, canned has about 300 IU/vitamin D
  • 3.5 oz mackerel, canned has about 250 IU/vitamin D
  • 3.5 oz tuna, canned has 236 IU/vitamin D
  • 3.5 oz shiitake mushrooms (fresh) has about 100 IU/vitamin D
  • 3.5 oz shiitake mushrooms (sun-dried) has about 1,600 IU/vitamin D
  • 1 egg yolk has about 20 IU/vitamin D
  • 8 oz fortified milk or yogurt has 100 IU/vitamin D
  • 8 oz fortified orange juice has about 100 IU/vitamin D
  • 3 oz fortified cheese has about 100 IU/vitamin D 
  • Excessive intakes of vitamin D can lead to high levels of calcium (hypercalcemia). The symptoms of this are weakness, confusion,constipation, loss of appetite, and development of painful calcium deposits. To avoid this, keep your supplement intake below the UL: