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Vitamin D deficiency linked to Parkinson’s disease, cognitive decline

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Studies of vitamin D have been on the rise in recent years, and with good reason—a 2009 estimate suggests that nearly three quarters of teens and adults in the U.S. are deficient in this vital nutrient. Vitamin D deficiency not only causes rickets, a skeletal disorder in which the bones are soft and weak, but has also been associated with a rapidly increasing range of chronic conditions like cancer, heart disease, and type 2 diabetes. Now, two new studies suggest a link between vitamin D and neurological disorder: Older people with insufficient vitamin D levels may be more likely to develop Parkinson’s disease and experience cognitive decline.

The first, led by Paul Knekt and colleagues at the National Institute for Health and Welfare, Finland, examined levels of vitamin D in the blood of 3,173 Finnish men and women aged 50 to 79 determined to be free of Parkinson’s disease at the start of the study. The researchers then examined the incidence of Parkinson’s disease in these participants over a 29-year follow-up period. They found that participants with the highest levels of vitamin D (more than 50 nmol/L) had a 65 percent lower risk of developing Parkinson’s disease than those with the lowest vitamin D levels (less than 25 nmol/L). The researchers accounted for potentially confounding variables such as age, sex, marital status, education, alcohol consumption, smoking, physical activity and month of blood draw.

Parkinson’s disease is a progressive neurodegenerative disorder that leads to impaired movement and speech, and is thought to result from insufficient dopamine levels in the brain. How vitamin D may protect against Parkinson’s is not understood, although there is limited evidence from cell-based and animal models that vitamin D may prevent the loss of dopaminergic neurons (cells that produce dopamine).

One important limitation to the study is that the average vitamin D concentration of all the study participants (approximately 40 nmol/L) falls well below what is considered to be optimal (more than 75 nmol/L). Therefore, whether supplementation with vitamin D would further lower the risk for Parkinson’s remains unknown. Nevertheless, the study suggests that not having enough vitamin D may predispose individuals to Parkinson’s, and provides a starting point for further investigation. The results were published online July 12 in the Archives of Neurology.

In the second study, David Llewellyn of the University of Exeter and colleagues examined vitamin D levels among 858 Italian men and women age 65 and older. They found that more than half of the participants with dementia were vitamin D deficient (less than 50 nmol/L). What’s more, cognitive tests revealed that severely deficient individuals (less than 25 nmol/L) were 60 percent more likely to undergo cognitive decline over the six-year follow-up period. This study appears online July 12 in the Archives of Internal Medicine.

Humans can obtain vitamin D by eating oily fish or fortified foods, and it is also photosynthesized in the skin upon exposure to adequate amounts of ultraviolet B (UVB) rays in sunlight. Major factors that influence vitamin D status in humans include season, latitude, age, skin tone, diet and supplement use. The U.S. Institute of Medicine currently recommends that adult men and women aim for a daily intake of 200 to 600 International Units (IU) of vitamin D.

New guidelines for vitamin D intake were published online July 12 in the Canadian Medical Association Journal by scientists from Osteoporosis Canada, a nonprofit organization. Because vitamin D influences calcium absorption and may protect against osteoporosis, the authors advise an increased daily intake of 400 to 1000 IU for healthy Canadians under age 50, and up to 2000 IU for those older than 50. The researchers state the changes are necessary because winter sunlight north of the 35th parallel (which coincides with the southern border of Tennessee) provides insufficient UVB for people living in that region to adequately make vitamin D.

The studies by Knekt and Llewellyn are not the first to link vitamin D deficiency with neurological problems, however. A role for vitamin D has previously been suggested in multiple sclerosis, autism and schizophrenia.

Some experts advise interpreting the results of these and other observational studies of vitamin D with caution. The above studies relied on participants from specific geographic areas, so more study is needed to determine whether the findings apply to other regions. Furthermore, "low vitamin D levels may simply be a marker for lower health status rather than a cause of it," Andrew Grey, professor of medicine at the University of Auckland, wrote in an editorial in the Archives of Internal Medicine. This is because vitamin D levels are directly related to sunlight exposure and physical activity; less healthy individuals are therefore likely to be less active and more sunlight-deprived, and have lower levels of vitamin D.

"It is now time to test the various hypotheses generated by observational studies of vitamin D…in adequately designed and conducted randomized controlled trials," Grey concluded. "We should invest in trials that provide the best possible evidence on the benefits and risks of vitamin D before we invest in costly, difficult, and potentially unrewarding interventional strategies."

Image courtesy of iStockPhoto

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  1. 1. manitouphotos 5:16 pm 07/13/2010

    I’m not a scientist, nor do I possess a scientific background. But, I’m interested in learning about science and enjoy reading about studies that are conducted to determine causes and preventions of diseases, especially since the spectrum of public health is so broad and complex yet so very important to our well being within society. I am always impressed with long term studies that span years and sometimes decades and commend those scientists who remain committed to find a means to an end, or at least finish a study in order to progress towards an end and collect important data like the one led by Paul Knekt over nearly 30 years.

    I’d be curious to know if Knekt and his team looked at, or at least took into account, the factor of skin color. In the past, some studies have shown that older adults with darker skin are at high risk of vitamin D deficiency. Because Finland is predominantly white, the study becomes affective for determining negative aspects of vitamin D deficiency in the caucasian population. But this story points out that more studies need to be done in varying geographic regions. Has there not been many studies involving caucasians exploring the issues of vitamin D deficiency other than this one? And have most studies until now involved people with darker skin? Forgive me for my lack of knowledge, but again I don’t have a scientific background unlike a lot of readers of Scientific American.

    I was glad to have read this story though, for it presented both sides of the research well and is informing us readers about important happenings within public health. I’ve worked at publications in the past and know there are lots of story ideas to choose from during editorial meetings. I appreciate that Scientific American is choosing to report on matters that directly affect and inform the public on important health topics.

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  2. 2. arunan 3:07 am 07/14/2010

    A study in south India, among the daily wage farm labourers will be a tempting proposition!

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  3. 3. gamt67 12:29 pm 07/14/2010

    I can not offer any additional references, but only wanted to comment on how humble and cordial your comments are compared to so many i read here and elsewhere; yours has given me hope that not all commentators are obnoxious and ignorant jerks, thank you.

    Link to this
  4. 4. ganne 1:56 pm 07/14/2010

    This article is very important for me. In fact, this is a wonderful website.

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  5. 5. katesisco 2:53 pm 07/14/2010

    A decade of research has led to new understanding of insomnia via the brain peptides orexins.
    Researchers at the Washington School of Med, St Louis, MO :
    "Orexin or compounds it interacts with may become new drug targets for treatment of Alzheimer’s disease," says senior author David M. Holtzman, M.D., the Andrew and Gretchen Jones Professor and chair of the Department of Neurology at the School of Medicine and neurologist-in-chief at Barnes-Jewish Hospital. "The results also suggest that we may need to prioritize treating sleep disorders not only for their many acute effects but also for potential long-term impacts on brain health."

    Link to this
  6. 6. wmroche 11:06 pm 07/15/2010

    Study shows links between low levels of vitamin D in pregnant women and increased incidence of multiple sclerosis in their children later in life.

    How Inuit who live all their lives in low sunlight environment get sufficient vitamin D from their diet of marine mammals and fish. They do not experience the same level of disease such as MS, diabetes, cancer, etc as we who live in more southern climes.

    But the benefits of vitamin D are no longer restricted to cancer prevention: Studies have linked a shortage of the compound to such serious, chronic ailments as multiple sclerosis, diabetes, heart disease, influenza and schizophrenia.

    Their are many articles advocating increasing ones intake of vitamin D either through increased exposure to sunlight as long as one’s shadow is shorter than you are tall (otherwise ozone layer blocks UVB that produces vitamin D). Or you can take a D supplement either through a pill or eating the organs of large sea mammals like the Inuit.

    "Either take "D" pill or move to Brazil"

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  7. 7. manolito 3:52 am 11/11/2010

    Here in Australia there is so much focus on the hole in the Ozone layer which is immediately above us, that campaigns onstantly urge people to cover up, and never venture out without an SP30 or higher sunblock. last winter I was diagnosed as Vitamin D deficient. I found a company called Inspired Wellbeing who sell Blooms Vitamin D3 1000IU 200 Capsules at a very competitive price.

    Vitamin D is required for the regulation of the minerals calcium and phosphorus found in the body. This regulation plays an important role in maintaining the proper bone structure and healthy teeth. Vitamin D helps with calcium absorption;

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  8. 8. manolito 3:54 am 11/11/2010

    If anyone is in Australia and would like to try a Vitamin D suppliment here is the link to <a href= "">Blooms Vitamin D3 1000IU 200 Capsules</a> from Inspired Wellbeing

    Link to this
  9. 9. pritih 4:04 am 02/10/2011

    Rickets is a bone disease, which retains only children and adolescents. It is caused by a failure of osteoid to calcify in a person at a time. The lack of osteoid to calcify in the adult is called osteomalacia. Vitamin D deficiency rickets occurs in metabolites of vitamin D. Less often, lack of calcium and phosphorus also lead to rickets. Vitamin D-3 (cholecalciferol) is formed in the skin of a derivative of cholesterol under the influence of ultraviolet-B light. Ultraviolet light or cod liver oil was the only significant source of vitamin D in early 1920, when ergosterol (vitamin D-2) was synthesized from irradiated plant steroids.

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  10. 10. Devrie 12:06 pm 03/20/2011

    I just found my new vitamin store and loaded up on vitamin D for my dad. The prices are the lowest I could find. They gave me a free gift of $5.00 with no minimum purchase and I got free shipping! The code I used at checkout is WIR500. Maybe it will work for you too?

    Link to this

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