Vitamin D has received a great deal of attention recently. Vitamin D has long been recognized as primarily a regulator of calcium and phosphorus, helping to protect bone density. In recent years, however, our understanding of the functions of vitamin D in the body has expanded. Vitamin D is now understood to play an important role in metabolic and immune system functions. Vitamin D deficiency has been linked to a number of illnesses and chronic conditions, including high blood pressure, diabetes, metabolic syndrome, pulmonary disease, and chronic pain.
We've seen evidence that vitamin D deficiency is associated with sleep problems, particularly with daytime sleepiness. A new study examined the link between daytime sleepiness and vitamin D, and also considered one of the major risk factors of vitamin D deficiency: skin pigmentation.
Researchers at Louisiana State University investigated the relationship between vitamin D and daytime sleepiness with two specific goals in mind. First, they wanted to determine whether a correlation exists between vitamin D levels in the body and excessive daytime sleepiness. Second, they sought to evaluate the role that race might play in the relationship between daytime sleepiness and vitamin D.
In earlier work, researchers at LSU had observed that more than half of the patients who came to their sleep clinic with sleep problems and with chronic pain were also deficient in vitamin D. They noticed this cluster of symptoms appeared to occur more often in patients who were African-American.
Vitamin D is actually a fat-soluble hormone that the body can receive in food and also through supplements. But the primary -- and most effective -- way the body accumulates vitamin D is during exposure to sunlight. Exposure to sunlight prompts our skin to self-manufacture vitamin D. Increased skin pigmentation lowers the rate of manufacture of vitamin D. Therefore, greater levels of skin pigmentation are considered a risk factor for vitamin D deficiency.
The Centers for Disease Control estimates that nearly one-third of African-Americans are deficient in vitamin D. Other groups at risk of vitamin D deficiency include the elderly, the obese, pregnant and lactating women, and people who receive limited exposure to the sun.
The LSU study involved 81 patients, all of whom had either sleep problems or musculoskeletal pain either in the day or the evening, or both. Sixty-five percent of the patients in the study were white, and 35 percent were African-American. All of the patients in the study group were diagnosed with a sleep disorder. Nearly three-quarters had obstructive sleep apnea, while others suffered from insomnia or restless leg syndrome. All patients were evaluated for excessive daytime sleepiness using the Epworth Sleep Scale, a standard measurement. Their levels of vitamin D were measured using blood tests.
The results of the study support a strong correlation between excessive daytime sleepiness and vitamin D. They also indicate that race is a factor in the relationship between vitamin D and daytime sleepiness. But the results were in some ways surprising and indicate a complicated relationship, particularly where race is concerned.
Here's an overview of the most important findings:
- Sixty-five percent of the study population was found to have a vitamin D deficiency.
- The patients with greater skin pigmentation had higher average levels of daytime sleepiness and lower average levels of vitamin D, compared to those with less skin pigmentation
- African-American patients made up 35 percent of the study population, but 55 percent of the group that was deficient in vitamin D
- Only 6 percent of the group without a vitamin D deficiency were African-American
- Among those with deficiencies of vitamin D -- under 20 mg/mL as measured by a blood test -- there was no correlation between vitamin D levels and daytime sleepiness. This is the opposite of what was expected based on prior research.
- An exception to this was found among African-American patients in the study group. Among those African-American patients with vitamin D deficiency, there was a direct correlation between levels of vitamin D and daytime sleepiness. Among these patients, higher vitamin D levels were associated with higher levels of daytime sleepiness -- the exact opposite of what was expected.
It is this last finding that is unexpected, and surprised researchers themselves, who expected to see lower levels of vitamin D associated with higher levels of daytime sleepiness.
Why might this have been the case? Additional research clearly is needed to further explore the role that skin pigmentation may play in vitamin D deficiency and its effect on sleep, and daytime sleepiness in particular. This was a small study, and larger-scale research may provide a clearer picture of this complicated relationship.
There are other important questions that arise. We can see an association between vitamin D deficiency and daytime sleepiness, but we don't have an understanding of cause and effect. Is vitamin D deficiency directly responsible for excessive daytime sleepiness and other sleep problems? Or is poor sleep a consequence of other medical conditions associated with vitamin D deficiency, such as chronic pain? What are the biological mechanisms by which vitamin D -- and a lack thereof -- affect sleep functions in the body? There's a lot we don't yet know about the relationship between vitamin D and sleep.
If you're at risk for vitamin D deficiency, talk to your doctor. Supplements, dietary changes, and safe and controlled exposure to sun can all help boost levels in the body. Making sure your body has sufficient levels of vitamin D offers important health protections and, perhaps, a welcome boost of energy in place of daytime sleepiness.
Michael J. Breus, PhD
The Sleep Doctor™
Everything you do, you do better with a good night's sleep™
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