Sleep disorders, vitamin D and skin pigmentation

This article discusses the link between vitamin D deficiency and the increase of the occurrence of sleep disorders.

Vitamin D Deficiency and Daytime Sleepiness: Skin Pigmentation Is a Complicated Factor

Posted: 01/30/2013 12:11 pm

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.

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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?    Full article HERE

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Michael J. Breus, PhD 
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Vitamin D deficiency linked with cognitive impairment in adults

This study shows that Vitamin D deficiency, or hypovitaminosis D, is linked with cognitive impairment in adults affecting their memory.

Hypovitaminosis D is associated with global cognitive impairment in adults. It remains unclear which domain–specific cognitive functions are affected with hypovitaminosis D. Lower serum 25OHD concentrations predict executive dysfunctions, especially on mental shifting, information updating and processing speed. The association with episodic memory remains uncertain.

Abstract

Background: Hypovitaminosis D is associated with global cognitive impairment in adults. It remains unclear which domain-specific cognitive functions are affected with hypovitaminosis D. Objective. To systematically review and quantitatively synthesize the association of serum 25-hydroxyvitamin D (25OHD) concentrations with episodic memory and executive functions in adults. Methods: A Medline and PsycINFO^®libraries search was conducted on May 2012, with no limit of date, using the Medical Subject Headings (MeSH) terms “Vitamin D” OR “Hydroxycholecalciferols” combined with the MeSH terms “Memory” OR “Memory Disorders” OR “Executive Function” OR “Attention” OR “Cognition” OR “Cognition disorders” OR “Dementia” OR “Alzheimer disease” OR “Neuropsychological Tests”. Fixed-effects meta-analysis was performed from 12 eligible studies using an inverse-variance method. Results: Of the 285 selected studies, 14 observational studies (including 3 prospective cohort studies) and 3 interventional studies met the selection criteria. All were of good quality. The number of participants ranged from 44–5,692 community-dwellers (0–100% women). In the pooled analysis, although episodic memory disorders showed only modest association with lower 25OHD concentrations (summary effect size of the difference (ES) = −0.09 [95%CI:−0.16;−0.03]), associations of greater magnitude were found with executive dysfunctions (processing speed: mean difference of Trail Making Test (TMT)-A score = 4.0 [95%CI:1.20;6.83]; mental shifting: mean difference of TMT-B score = 12.47 [95%CI:6.78;18.16]; information updating tests: ES = −0.31 [95%CI:−0.5;−0.09]). The pooled risk of incident decline of TMT-B score was OR = 1.25 [95%CI:1.05;1.48] in case of initial lower 25OHD concentrations. Vitamin D repletion resulted in improved executive functions (ES = −0.50 [95%CI:−0.69;−0.32] for before-and-after comparison), but exhibited no difference with control groups (ES = 0.14 [95%CI:−0.04;0.32] for between-group comparison after intervention). Conclusion: Lower serum 25OHD concentrations predict executive dysfunctions, especially on mental shifting, information updating and processing speed. The association with episodic memory remains uncertain.

Methods

• A Medline and PsycINFO libraries search was conducted on May 2012, with no limit of date, using the Medical Subject Headings (MeSH) terms “Vitamin D” OR “Hydroxycholecalciferols” combined with the MeSH terms “Memory” OR “Memory Disorders” OR “Executive Function” OR “Attention” OR “Cognition” OR “Cognition disorders” OR “Dementia” OR “Alzheimer disease” OR “Neuropsychological Tests”.
• Fixed–effects meta–analysis was performed from 12 eligible studies using an inverse–variance method.

Results

• Of the 285 selected studies, 14 observational studies (including 3 prospective cohort studies) and 3 interventional studies met the selection criteria.
• All were of good quality. The number of participants ranged from 44–5,692 community–dwellers (0–100% women).
• In the pooled analysis, although episodic memory disorders showed only modest association with lower 25OHD concentrations (summary effect size of the difference (ES) = –0.09), associations of greater magnitude were found with executive dysfunctions (processing speed: mean difference of Trail Making Test (TMT)–A score = 4.0 [95%CI:1.20;6.83]; mental shifting: mean difference of TMT–B score = 12.47 [95%CI:6.78;18.16]; information updating tests: ES = –0.31).
• The pooled risk of incident decline of TMT–B score was OR = 1.25 [95%CI:1.05;1.48] in case of initial lower 25OHD concentrations.
• Vitamin D repletion resulted in improved executive functions, but exhibited no difference with control groups (ES = 0.14 [95%CI:–0.04;0.32] for between–group comparison after intervention).

Read more here