We're nearing the end of what's been a long winter for people in many parts of the United States. In the middle and northern regions of the U.S., where winter brings not only cold but limited sun, people aren't only deprived of warmth, they also may be deficient in an important nutrient: Vitamin D.
The body actually produces its own Vitamin D, in response to exposure to sunlight. For this reason, Vitamin D isn't actually considered a vitamin at all, but rather is classified as a hormone. Besides sun exposure, people also receive Vitamin D through foods -- fatty fish and fish oils, egg yolks, as well as fortified foods like dairy and juice -- and also from supplements.
Unfortunately, many people don't maintain sufficient levels of Vitamin D--and this can lead to health complications. It's estimated that 50 percent or more of adults and children may be deficient in Vitamin D, which is now widely recognized as a public health problem.
Vitamin D is critical to the body's mental and physical function. It assists the body in absorbing calcium and phosphorus, and contributes to bone health. Healthy levels of Vitamin D may help with weight loss and weight management. Research suggests that low levels of Vitamin D are associated with higher risks for several serious diseases, including cancer, diabetes, cardiovascular disease, and multiple sclerosis. Insufficiency of Vitamin D is also linked to greater risk for depression and other mood disorders. In healthy people, maintaining higher levels of Vitamin D may offer protection against these same conditions.
Vitamin D may also be important for maintaining healthy sleep. Recent research indicates that Vitamin D may influence both sleep quality and sleep quantity. Researchers analyzed the sleep patterns and Vitamin D levels among a group of older adult men, and found that Vitamin D deficiency was associated with less sleep overall and also with more disrupted sleep. The study included 3,048 men ages 68 and older. Researchers measured Vitamin D serum levels using a blood test. They measured sleep using wrist actigraphy, recording measurements of total sleep time, wake time after sleep onset, and sleep efficiency--a measurement that results from comparing time spent in bed to the time actually spent sleeping.
Among participants, 16 percent had low levels of Vitamin D. To identify the possible influence of Vitamin D over sleep, researchers controlled for several other factors, including age, season of the year, other health conditions, body-mass index, and both physical and cognitive function. They found that low levels of Vitamin D were linked to several problems with sleep:
• Low Vitamin D increased the likelihood that participants experienced insufficient sleep, sleeping less than five hours a night.
• Low levels of Vitamin D were linked to lower sleep efficiency scores, and a greater chance of scoring below 70 percent. A healthy sleep efficiency score is generally considered to be 85 percent or higher.
A lower sleep efficiency score is an indicator of difficulties with sleep quality, as well as perhaps with sleep quantity. A low sleep efficiency score may mean it takes a long time to fall asleep or may indicate waking very early. A low sleep efficiency can also mean sleep is fragmented and restless, with many awakenings throughout the night.
This study is noteworthy because it appears to be the first study to objectively show that Vitamin D deficiency has negative effects on sleep. Other research has demonstrated links between low levels of Vitamin D and sleep problems. But these studies have measured sleep subjectively, using survey data and reports from participants who assess their own sleep, in terms of both quality and quantity. This study measured sleep using objective tools -- specifically wrist sensors -- before analyzing that data in relation to levels of Vitamin D.
Overall, there's not been enough research devoted to this relationship--likely a complicated one -- between Vitamin D and sleep. The results of this study ought to encourage more attention and focus on this relationship and its potential influence over long-term health.
What's the best way to increase your Vitamin D? There's no better source than the sun. Direct sun exposure to skin triggers the synthesis of Vitamin D. But sun exposure can't always be relied upon for a steady, consistent source of Vitamin D. There are a number of factors that can influence how effectively sun exposure can trigger Vitamin D production in the body, including air pollution, time of day, season of the year, and level of cloud cover. Sunscreen and clothing can also impede the effects of sun exposure for Vitamin D. People with higher levels of skin pigmentation absorb less of the UVB rays necessary to begin the synthesis of Vitamin D, and may be more likely to have low levels as a result. Older adults are also at greater risk for low Vitamin D levels.
Protecting your skin from excessive sun exposure is important--I am not suggesting you abandon wearing sunscreen. But some limited time in the sun without sunscreen to allow for Vitamin D production may be useful for health, and for sleep. The recommendations for sun exposure to boost Vitamin D generally fall in the range of 5-10 minutes of exposure, from a few times a week to daily.
Adding Vitamin D rich and fortified foods to your diet can also help increase levels. Fatty fish like salmon, tuna, swordfish, and sardines are all excellent sources of Vitamin D. So are eggs. Many dairy products, including milk and yogurt, are fortified with Vitamin D, as are citrus juices and many cereals. Supplements are another important option to help you maintain healthy Vitamin D levels, especially for people who are at high risk for deficiency, because of age, ethnicity, health conditions, or where they live.
The best way to know if your Vitamin D levels are low is to have your physician perform a blood test. If like so many people, your levels are low, you and your doctor can put together a plan that may include diet, controlled sun exposure, and supplements, to bring levels up and make sure they stay that way. Maintaining sufficient levels of Vitamin D is good for overall health wellness, and likely also to be good for your sleep.
Michael J. Breus, PhD
The Sleep Doctor™
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