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Tag: blood levels of 25-hydroxyvitamin D

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Again, more benefits of vitamin D. Think of it as the sunshine vitamin, but supplements also work, especially vitamin D3 (rather than D2). This time higher levels of vitamin D in the blood (as measured by the vitamin D biomarker, 25-hydroxyvitamin D [25(OH)D) are linked to lower incidence of macular degeneration among those women genetically prone to it.

Macular degeneration is thought to have both genetic (inherited) and environmental components. Currently macular degeneration is the leading cause of vision loss and affects about 2.07 million Americans (this is according to the National Eye Institute). Note that this number is very different than that given by the American Macular Degeneration Foundation in the article. From Medical Xpress:

Vitamin D may play key role in preventing macular degeneration

Vitamin D has been studied extensively in relation to bone health as well as cancer. Now, a team led by a researcher at the University at Buffalo has discovered that vitamin D may play a significant role in eye health, specifically in the possible prevention of age-related macular degeneration, or AMD, among women who are more genetically prone to developing the sight-damaging disease.

In a paper published today (Aug. 27) in JAMA Ophthalmology online, Amy Millen, associate professor of epidemiology and environmental health in UB's School of Public Health and Health Professions, and her team found that women who are deficient in vitamin D and have a specific high-risk genotype are 6.7 times more likely to develop AMD than women with sufficient vitamin D status and no high risk genotype.

Macular degeneration is characterized by the deterioration of the macula, a small part of the central retina where the eye's photoreceptors (rods and cones) are most highly concentrated. The leading cause of legal blindness, macular degeneration affects more than 10 million Americans—more than cataracts and glaucoma combined—according to the American Macular Degeneration Foundation. The disease affects a person's central vision, which is needed for common tasks such as reading and driving. The effect is similar to that of a rain drop on the center of a camera lens.

Researchers analyzed data compiled on 1,230 women ages 54 to 74 who participated in the Carotenoids in Age-related Eye Disease Study (CAREDS),..... CAREDS was conducted among participants at three of the centers: University of Wisconsin (Madison), the University of Iowa (Iowa City) and the Kaiser Center for Health Research (Portland, Oregon). Researchers were able to determine participants' vitamin D status by analyzing serum samples for a vitamin D biomarker, 25-hydroxyvitamin D [25(OH)D], which provided a glimpse into vitamin D intake through all sources: diet, supplements and sunlight.

Human skin can synthesize vitamin D when exposed to ultraviolet light, Millen explains. However, for many people, 15 to 30 minutes a day with 10 percent of their skin exposed might be sufficient. In winter months, when there is a lower solar angle, sun exposure may not be not sufficient to maintain blood level for people who live north of a line from about Washington, D.C., to Los Angeles. At these times and locations, dietary intake may be needed. Dietary sources of vitamin D include fortified foods such as milk and foods that naturally contain vitamin D such as fatty fish like salmon and mackerel.

"Macular degeneration has been found to be strongly associated with genetic risk," Millen says. Among many genes linked to AMD, one of the strongest is a specific genetic variant (Y402H) in the complement factor H gene, called CFH for short. This gene codes for the CFH protein that is involved in the body's immune response to destroy bacteria and viruses. Inflammation is believed to be involved in the development of macular degeneration.  "People who have early stage AMD develop drusen, lipid and protein deposits that build up in the eye. Your body sees this drusen as a foreign substance and attacks it, in part via the complement cascade response," explains Millen.

Vitamin D shows promise for protecting against because of its anti-inflammatory and antiangiogenic properties; antiangiogenic refers to slowing the growth of new blood vessels, often seen in late stages of AMD."Our message is not that achieving really high levels of vitamin D are good for the eye, but that having deficient vitamin D levels may be unhealthy for your eyes," Millen says. 

Although the odds of having AMD was higher in women who were deficient for vitamin D, with 25(OH)D levels below 12 ng/mL (30 nmol/L), increasing vitamin D levels beyond 12 ng/mL did not further lower the odds of AMD to any meaningful extent, she explains.

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Low levels of vitamin D are associated with low levels of testosterone in healthy middle-aged men. Note that hypovitaminosis D means low levels of vitamin D in the blood, defined by a lab test as "25-hydroxyvitamin D level below 30.0 ng/L. Interestingly, being overweight also seems to lower the testosterone level, and losing weight raises the level, and supplementing with vitamin D may raise the testosterone level in those with low levels (the German study mentioned in the article). And research with mice suggests that there is something about testosterone synthesis that needs vitamin D. From Medscape:

Low Vitamin D Tied to Testosterone Dip in Healthy Men

Low levels of vitamin D are significantly and independently associated with low levels of testosterone in otherwise healthy middle-aged men, according to a study presented at the American Urological Association 2015 Annual Meeting in New Orleans. 

In this new analysis of data from of the World Trade Center CHEST program, blood samples from 824 men were analyzed for various parameters, such as 25-hydroxyvitamin D and total testosterone. Hypovitaminosis D was defined as a 25-hydroxyvitamin D level below 30.0 ng/L.

Level of 25-hydroxyvitamin D were insufficient in 68% of the samples....Total testosterone was higher in men with normal levels of 25-hydroxyvitamin D than in men with lower levels...."subjects with hypovitaminosis D still had significantly lower total testosterone than those with normal total testosterone (P = .019)," Dr McLaughlin and her colleagues report. When levels of 25-hydroxyvitamin D were lower, body mass index was higher than when levels were normal (30.8 vs 29.12 kg/m²; P < .001), waist circumference was greater (41.3 vs 39.8 inches; P < .001), and lipid profiles were less favorable.

In previous studies, testosterone levels were shown to be lower in mice who had the vitamin D receptor genetically deleted, said Dr McLaughlin."This suggests that there is something about testosterone synthesis that needs vitamin D," she explained.

In a small German study of healthy overweight men with a low baseline level of 25-hydroxyvitamin D and testosterone levels at the lower end of the reference range, there was a significant increase in total testosterone levels after 12 months of vitamin D 3000 IU daily (Horm Metab Res. 2011;43:223-225)...the German study was primarily a weight-loss study, and weight loss in and of itself causes increases in testosterone."We see that in patients who undergo bariatric surgery to remove visceral fat," he explained. "Once the weight loss has taken place, their testosterone levels normalize independent of anything else."

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The possibility of lowering the risk of ischemic stroke (and poor recovery from it) is a good reason to try to increase vitamin D levels - by supplements and/or sunlight. Note that an ischemic stroke occurs when a blood vessel that supplies blood to the brain is blocked by a blood clot. From Medical Xpress:

Low vitamin D predicts more severe strokes, poor health post-stroke

Stroke patients with low vitamin D levels were found to be more likely than those with normal vitamin D levels to suffer severe strokes and have poor health months after stroke, according to research presented at the American Stroke Association's International Stroke Conference 2015. Low vitamin D has been associated in past studies with neurovascular injury (damage to the major blood vessels supplying the brain, brainstem, and upper spinal cord).

"Many of the people we consider at high risk for developing stroke have low vitamin D levels. Understanding the link between stroke severity and vitamin D status will help us determine if we should treat vitamin D deficiency in these high-risk patients," said Nils Henninger, M.D., senior study author and assistant professor of neurology and psychiatry at University of Massachusetts Medical School in Worchester.

Henninger and colleagues studied whether low blood levels of 25-hydroxyvitamin D, a marker of vitamin D status, is predictive of ischemic stroke severity and poor health after stroke in 96 stroke patients treated between January 2013 and January 2014 at a U.S. hospital. They found:

  • Overall, patients who had low vitamin D levels –defined as less than 30 nanograms per milliliter (ng/mL) – had about two-times larger areas of dead tissue resulting from obstruction of the blood supply compared to patients with normal vitamin D levels.
  • This association was similar among patients who suffered lacunar strokes (in which the small, intricate arteries of the brain are affected) and patients with non-lacunar strokes (such as those caused by carotid disease or by a clot that originated elsewhere in the body).
  • For each 10 ng/mL reduction in vitamin D level, the chance for healthy recovery in the three months following stroke decreased by almost half, regardless of the patient's age or initial stroke severity.