Vitamin D Can Save You from Diabetes and Dementia

Vitamin D Levels

Story at-a-glance

  • Low vitamin D levels may be an even larger factor in type 2 diabetes than obesity
  • Among obese people, those without metabolic disorders like type 2 diabetes had higher levels of vitamin D than those with such disorders
  • Among lean people, those with metabolic disorders were more likely to have low levels of vitamin D


This is an older article that may not reflect Dr. Mercola’s current view on this topic. Use our search engine to find Dr. Mercola’s latest position on any health topic.

By Dr. Mercola

Do you know your vitamin D level? If not, a simple blood test called 25(OH)D, or 25-hydroxyvitamin D, can reveal your levels and give you incredible insight into your potential future risk of disease.

Low vitamin D levels are widely known to harm your bones, leading them to become thin, brittle, soft, or misshapen. But a lack of vitamin D does not only impact your bones. Far from it.

You see, vitamin D isn’t a vitamin at all. It’s a steroid hormone that influences virtually every cell in your body. From your heart to your brain to your immune system, maintaining optimal vitamin D levels is incredibly important.

It’s also incredibly easy, because the best way to get vitamin D is to have regular exposure to the sun or a high-quality tanning bed. If those aren’t options, you can take vitamin D3 orally (along with some synergistic nutrients, which I’ll discuss below). It’s one of the least expensive vitamin supplements…

The point is, there’s no reason to put your health at risk from low vitamin D levels… yet researchers such Dr. Michael Holick estimate that 50 percent of the general population is at risk of vitamin D deficiency and insufficiency.

If you’re among them, new research shows your risk of diabetes and other metabolic disorders may be significantly increased.

Vitamin D Deficiency Linked to Diabetes

You’re probably aware that obesity is associated with type 2 diabetes, but a new study found low vitamin D levels may be an even more significant factor. In a study of more than 100 people, those with low vitamin D levels were more likely to have type 2 diabetes, pre-diabetes, or metabolic syndrome, regardless of their weight.

Among obese people, those without metabolic disorders had higher levels of vitamin D than those with such disorders. And among lean people, those with metabolic disorders were more likely to have low levels of vitamin D. According to one of the study’s authors:1

"Our findings indicate that vitamin D is associated more closely with glucose metabolism than obesity…

The study suggests that vitamin D deficiency and obesity interact synergistically to heighten the risk of diabetes and other metabolic disorders. The average person may be able to reduce their risk by maintaining a healthy diet and getting enough outdoor activity."

It’s not the first time vitamin D has been shown to play a role in diabetes. One Indian study found that vitamin D and calcium supplementation in combination with exercise can prevent pre-diabetes from progressing into full-blown diabetes. For every unit increase in vitamin D levels, the risk of progression to diabetes in people with pre-diabetes went down by 8 percent.2

The Diabetes-Dementia Connection… And What Vitamin D Has to Do with It

Faulty insulin (and leptin, another hormone) signaling is an underlying cause of insulin resistance, which, of course, typically leads to type 2 diabetes.

However, while insulin is usually associated with its role in keeping your blood sugar levels in a healthy range, it also plays a role in brain signaling. When researchers disrupted the proper signaling of insulin in the brain, it resulted in dementia.3

Researchers have also been looking into factors that might play a role in mild cognitive impairment (MCI) worsening into dementia. People with MCI, which can interfere with your ability to think and remember things, have a greater risk of developing dementia… but not everyone with MCI does.

A new study has revealed several potential factors, including diabetes. People with MCI and diabetes were at a greater risk of MCI progressing to dementia.4 Past research has also shown that diabetes is linked to a 65 percent increased risk of developing Alzheimer's.5

This may be due, in part, because insulin resistance and/or diabetes appear to accelerate the development of plaque in your brain, which is a hallmark of Alzheimer's.6

Other research has found that impaired insulin response was associated with a 30 percent higher risk of Alzheimer's disease,7 and overall dementia and cognitive risks were associated with high fasting serum insulin, insulin resistance, impaired insulin secretion and glucose intolerance.

We also have growing evidence that low vitamin D levels play a role in diabetes, which in turn might also play a role in your brain health. However, dementia is also directly linked to vitamin D.

Seniors who have low vitamin D levels may double their risk of dementia, including Alzheimer's disease.8 As noted by the authors, "This adds to the ongoing debate about the role of vitamin D in nonskeletal conditions."

Optimal Vitamin D Levels Help You Fight the Flu

Vitamin D also fights infections, including colds and the flu, as it regulates the expression of genes that influence your immune system to attack and destroy bacteria and viruses. New research in India showed that vitamin D helped suppress inflammatory response to H1N1 “swine flu.”9

A study done in Japan also showed that schoolchildren taking 1,200 units of vitamin D per day during the winter reduced their risk of getting influenza A infection by about 40 percent. I believe it's far more prudent, safer, less expensive, and most importantly, far more effective to optimize your vitamin D levels than to get vaccinated against the flu. According to Dr. Holick:

“We know that the immune cells use vitamin D and that they activate vitamin D. There's good evidence that it will help kill tuberculosis bacteria, for example, if you have adequate vitamin D on board... We think that the immune system is primed with vitamin D in order to help fight infections."

In addition, in a large study involving about 19,000 Americans, people with the lowest vitamin D levels reported having significantly more recent colds or cases of the flu -- and the risk was even greater for those with chronic respiratory disorders like asthma.10 At least five additional studies also show an inverse association between lower respiratory tract infections and vitamin D levels.

What Else Is Vitamin D Good For?

Download Interview Transcript

Researchers have pointed out that increasing levels of vitamin D3 among the general population could prevent chronic diseases that claim nearly 1 million lives throughout the world each year. Incidence of several types of cancer could also be slashed in half.

As mentioned by Dr. Holick, one of the Nurses’ Health Studies showed that nurses who had the highest blood levels of 25-hydroxyvitamin D, averaging about 50 ng/ml, reduced their risk of developing breast cancer by as much as 50 percent.

Similarly, a Canadian study done by Dr. Knight showed that women who reported having the most sun exposure as a teenager and young adult had almost a 70 percent reduced risk of developing breast cancer. In the interview above, Dr. Holick expands on these and many other health benefits of vitamin D. For instance, optimizing your vitamin D levels can help protect against:

  • Cardiovascular disease. Vitamin D is very important for reducing hypertension, atherosclerotic heart disease, heart attack, and stroke.
  • According to Dr. Holick, one study showed that vitamin D deficiency increased the risk of heart attack by 50 percent. What’s worse, if you have a heart attack and you’re vitamin-D deficient, your risk of dying from that heart attack creeps up to nearly 100 percent!

  • Autoimmune diseases. Vitamin D is a potent immune modulator, making it very important for the prevention of autoimmune diseases, like multiple sclerosis and inflammatory bowel disease.
  • Infertility. Vitamin D may help stimulate the production of hormones including testosterone and progesterone. In addition vitamin D is associated with semen quality in men and may improve menstrual frequency in women with polycystic ovary syndrome (PCOS).11
  • DNA repair and metabolic processes. One of Dr. Holick’s studies showed that healthy volunteers taking 2,000 IUs of vitamin D per day for a few months upregulated 291 different genes that control up to 80 different metabolic processes, from improving DNA repair to having effect on autoxidation (oxidation that occurs in the presence of oxygen and /or UV radiation, which has implications for aging and cancer, for example), boosting your immune system, and many other biological processes.

Vitamin D Isn’t the Only Benefit of Sun Exposure

Part of the reason why I recommend getting your vitamin from the sun, as opposed to orally, is because you’ll reap additional benefits above and beyond the vitamin D. Ultraviolet (UV) radiation has been used since ancient times to treat various diseases, and it’s known that a large number of molecules in your skin interact with and absorb UV.12 Peter Robert Ebeling, head of the department of medicine, School of Clinical Sciences and professor of medicine at Monash University, suggests that sunshine may have unknown health effects, such as impacting your body’s biological rhythms, reducing physical stresses on your body’s cells, and increasing heat production.

Sun exposure also alters the activity of your immune system in a way that reduces inflammation and likely helps protect against certain inflammatory diseases.13 Evidence presented in the journal Dermato-Endocrinology also confirmed that exposure to the sun in appropriate and measured timeframes has a number of health benefits unrelated to vitamin D production, such as:14

Enhancing mood and energy through the release of endorphins Protecting against and suppressing symptoms of multiple sclerosis (MS)
Treating skin diseases, such as psoriasis, vitiligo, atopic dermatitis, and scleroderma. UV radiation also enhances skin barrier functions Inducing nitric oxide (NO), which helps protect your skin against UV damage and offers cardiovascular protection, promotes wound healing through its antimicrobial effect, and has some anti-cancer activity
Melatonin regulation through the "third eye" of the pineal gland photoreceptors Relieving fibromyalgia pain
Standard treatment for tuberculosis 100 years ago, long before the advent of antibiotics Treating neonatal jaundice
Can be used to sterilize your armpits and eliminate the cause of most body odor Treating Seasonal Affective Disorder (SAD)
Synchronizing important biorhythms through sunlight entering your eye and striking your retina Regulating body temperature
Protecting against melanoma and decreasing mortality from it May be effective in treating T Cell lymphoma

FDA Looking for More Data Before Approving Sunscreen Additives

After years of review, the US Food and Drug Administration (FDA) said it still needs more information before it can confirm the safety and effectiveness of two new sunscreen ingredients, ecamsule and enzacamene. Unfortunately, they have already approved some other additives that are known to be toxic. Oxybenzone, for instance, is believed to cause hormone disruptions and cell damage that may provoke cancer.

In fact, two-thirds of the sunscreens analyzed by the Environmental Working Group (EWG) did not work well or contained potentially hazardous ingredients.15 In lieu of the skin-penetrating hormone-disrupting chemicals like oxybenzone, the safer sunscreens tended to use non-nanoparticle sized zinc- and titanium-based mineral ingredients, which block the sun's rays without penetrating your skin. You can also wear long-sleeved clothing and a hat to protect your skin from the sun in times when overexposure is a concern.

But remember, one of the greatest risks of sunscreen is that it blocks your body’s ability to produce vitamin D. You should use a natural sunscreen only after you’ve maxed out your daily vitamin D production, and even then consider using shade or clothing to block the sun. Shielding your face from the sun is a habit I recommend, as this will help keep it looking youthful longer. Your face, which is the most important cosmetic component of your body, is a relatively small surface area, so shielding it while exposing large portions of your body instead, is not going to make a big difference in terms of vitamin D production. This is why most cultures have traditionally worn a hat when in the sun.

How to Optimize Your Vitamin D Levels

I believe sensible sun exposure is the ideal way to optimize your vitamin D levels. As a general rule, you’ll want to expose large amounts of bare skin to the sun until it turns the lightest shade of pink, if you’re light-skinned. This typically occurs in about half the time it would normally take you to burn. So if you know you tend to get sunburned after 30 minutes, you’d want to stay in the sun for about 15 minutes. Those with darker skin may need to pay closer attention to notice when this slight reddening occurs. It’s nearly impossible to give any firm recommendations for how long you need to stay in the sun to optimize vitamin D production, as it varies greatly depending on a number of factors, such as:

Antioxidant levels and diet in general Age
Skin color and/or current tan level Use of sunscreen
Latitude and altitude (elevation) Cloud cover and pollution
Ozone layer Surface reflection
Season Time of day

If you can't get enough sensible sun exposure, then a high-quality tanning bed is your next best option. If your circumstances don't allow you to access the sun or a high-quality tanning bed, then you really only have one option if you want to raise your vitamin D, and that is to take a vitamin D3 supplement. As a general guideline, research by GrassrootsHealth suggests that adults need about 8,000 IUs per day to achieve a serum level of 40-60 ng/ml. If you do opt for a vitamin D supplement, please remember that you also need to boost your intake of vitamin K2 through food and/or a supplement, as well as get your levels tested to be sure you’re safely within the therapeutic range.

vitamin d levels chart

How Vitamin D Performance Testing Can Help Optimize Your Health

A robust and growing body of research clearly shows that vitamin D is absolutely critical for good health and disease prevention. Vitamin D affects your DNA through vitamin D receptors (VDRs), which bind to specific locations of the human genome. Scientists have identified nearly 3,000 genes that are influenced by vitamin D levels, and vitamin D receptors have been found throughout the human body. Is it any wonder then that no matter what disease or condition is investigated, vitamin D appears to play a crucial role? This is why I am so excited about the D*Action Project by GrassrootsHealth. Dr. Heaney is the Research Director of GrassrootsHealth and is part of the design of the D*action Project as well as analysis of the research findings.

GrassrootsHealth shows how you can take action today on known science with a consensus of experts without waiting for institutional lethargy. It has shown how by combining the science of measurement (of vitamin D levels) with the personal choice of taking action and, the value of education about individual measures that one can truly be in charge of their own health. In order to spread this health movement to more communities, the project needs your involvement. This was an ongoing campaign during the month of February, and will become an annual event.

To participate, simply purchase the D*Action Measurement Kit and follow the registration instructions included. (Please note that 100 percent of the proceeds from the kits go to fund the research project. I do not charge a single dime as a distributor of the test kits.) As a participant, you agree to test your vitamin D levels twice a year during a five-year study, and share your health status to demonstrate the public health impact of this nutrient. There is a $65 fee every six months for your sponsorship of this research project, which includes a test kit to be used at home, and electronic reports on your ongoing progress. You will get a follow up email every six months reminding you "it's time for your next test and health survey."

Vitamin D Kit
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