The long, dark days of another winter have come and gone. Tens of millions of Americans would be surprised to learn that winter has left them deficient in vitamin D. Your chances of being one of them are probably much greater than you imagine.
Vitamin D is synthesized in the skin in response to sunlight exposure, but few people achieve optimal levels this way, in part due to the limited ultraviolet light available during the winter months. This seasonal deficit is compounded by the fact that many people avoid sun exposure during the spring and summer months because of concern about premature skin aging and cancers like melanoma. Alarming new research suggests that these factors are contributing to a year-round epidemic of vitamin D deficiency, particularly in elderly adults.
Vitamin D does far more than promote healthy teeth and bones. Its role in supporting immunity and modulating inflammation make the consequences of vitamin D deficiency potentially devastating. A growing number of scientists who study vitamin D levels in human populations now recommend annual blood tests to check vitamin D status.
In this article, we examine the factors that contribute to the widespread prevalence of vitamin D deficiency, the latest studies supporting vitamin D’s critical role in preventing disease, and how much supplemental vitamin D you need to achieve optimal blood levels.
Vitamin D Deficiency: An Overlooked Epidemic
Vitamin D is a fat-soluble prohormone-that is, it has no hormone activity itself, but is converted to a molecule that does, through a tightly regulated synthesis mechanism. Its two major forms are vitamin D2 (or ergocalciferol) and vitamin D3 (or cholecalciferol). Vitamin D also refers to metabolites and other analogues of these substances. Vitamin D3 is produced in skin exposed to sunlight, specifically ultraviolet B radiation.
While vitamin D is best known for promoting calcium absorption and bone health, researchers have recently discovered important new roles for this versatile vitamin.1
As an active hormone,2
vitamin D is now seen as playing a central role in controlling immunity and inflammation,1,3,4
two vital processes that are tied to a host of age-related disease conditions.5-10
Just as scientists are discovering critical new roles for vitamin D, they are also finding that shockingly few people have blood levels of vitamin D adequate to support their daily needs.5,6
One leading researcher has referred to this deficit as a “vitamin D epidemic.”7
Estimates of the percentage of US adolescents and adults who are vitamin D deficient range from 21% to 58%,11
while as many as 54% of homebound older adults are believed to be vitamin D deficient.12
Because vitamin D3 is obtained in humans primarily as a result of exposure to sunlight,8
this puts people living outside the tropics at particular risk for vitamin D deficiency, especially from late fall to early spring.9
Further compounding the problem, many public health officials are concerned that their warnings about avoiding the sun because of skin cancer risk may in fact be causing people to limit their sun exposure to an unhealthy extent.10,13
Because sun exposure does pose significant health risks, and most Americans live outside of the regions where they can get adequate sun in winter, perhaps the best way to address this dilemma is by paying close attention to your blood levels of vitamin D and optimizing them through appropriate supplementation. Life Extension recommends that adults check their blood levels and supplement with enough vitamin D3 to achieve optimal blood levels.6-8
To meet all of the body’s needs for proper vitamin D activity, many scientists now advocate supplementing with doses that are considerably higher than the minimums currently recommended by the Institute of Medicine.14
While vitamin D can be obtained through a few dietary sources such as fish, eggs, and dairy products, these foods fail to provide the daily levels required by most individuals, thus necessitating vitamin D supplementation.
How Vitamin D Controls Cell Functions
Vitamin D’s applications in promoting optimal health stem from its ability to control production of vital proteins by switching genes on and off, and thus helping to determine the fate of cells. Cells affected by the active form of vitamin D, known as calcitriol,15-17
stop growing and reproducing, and rapidly mature into their final forms.3,4,17,18
Because of its unique ability to switch cell functions on and off, vitamin D has a dual effect that can modulate immune function3
by both boosting deficient immune function and quieting overactive autoimmunity.28
Vitamin D may further help to reduce the excessive inflammation and oxidative damage implicated in conditions such as osteoarthritis,29,30
chronic obstructive pulmonary disease (such as emphysema),31-33
and metabolic syndrome.36,37
Low vitamin D levels are linked to increased risk for all these conditions,38-46
highlighting the importance of regular vitamin D blood tests to detect and correct deficiencies before they contribute to the onset of disease.
Vitamin D: What You Need to Know
Ensuring Optimal Vitamin D Levels
Low dietary intake and limited sun exposure have led to an epidemic of vitamin D deficiency. Health experts now advise adults to regularly check their blood levels of vitamin D and to address deficiencies with supplemental vitamin D.
Vitamin D plays many essential roles throughout the body-enhancing calcium absorption, contributing to healthy bone mass, supporting immune function, and quelling inflammation.
Vitamin D quells inflammation that may exacerbate chronic heart failure, and in combination with other nutrients, benefits people with chronic heart failure. Vitamin D also shows promise in preventing both type I and type II diabetes, and offers important support for immune health. Vitamin D may help prevent wound infections and flu, support the body’s defense against tuberculosis, and boost immune function in patients with kidney failure.
Vitamin D likewise may help to alleviate seasonal affective disorder (SAD), a type of depression experienced during the winter months due to decreased sunlight.
Health experts urge all adults to have regular (at least annual) checks of vitamin D levels in their blood.7
There is a good chance that you will be deficient for at least part of the year if you live in North America, according to those experts.6,55
Once a deficiency is identified, supplementation can safely restore levels to the normal range. Checking vitamin D status again after a few months of supplementation is also advised.
While the federal government’s recommended dietary allowance (RDA) of vitamin D is 400 IU (10 mcg) daily,83
many health experts now advise daily doses of at least 800 IU (20 mcg) of vitamin D.84
Life Extension recommends that healthy adults supplement each day with at least 1000 IU of vitamin D. Elderly adults may benefit from higher doses such as 2000 IU daily, and even up to 5000 IU daily. Research published over the last decade suggests that vitamin D toxicity is unlikely at daily intake levels of less than 10,000 IU (250 mcg).14,85-88
Comprehensive research reviews conducted by a leading authority on vitamin D, Dr. Michael Holick, suggest that a healthy serum level of vitamin D (25-hydroxyvitamin D) is 75-125 nmol/L. Serum levels within this range have been associated with improved bone health and muscle strength.6,7,89
As with many supplements, an appropriate dosage is critical for efficacy and safety. Long-term supplementation with very high doses of vitamin D can cause dangerous elevations in blood calcium levels.90,91
Too much calcium in the blood can rapidly cause poor muscle and nerve function,92
and long-term elevations increase the risk of kidney stones.93
Anyone taking extremely high doses of vitamin D should be monitored for signs and symptoms of vitamin D toxicity, which include nausea, vomiting, poor appetite, constipation, weakness, heart arrhythmias, kidney stones, and elevated blood levels of cholesterol, calcium, or liver enzymes.83,84
Vitamin D is contraindicated in individuals with hypercalcemia (high blood calcium levels).83,84
People with kidney disease and those who use digoxin or other cardiac glycoside drugs should consult a physician before using supplemental vitamin D.83,84
Life Extension recommends that all adults check their blood vitamin D levels at least once a year. If levels are low, discuss supplementation with your health care provider, and then follow up with repeat testing after a few months.
Vitamin D May Help Prevent Diabetes
Exciting research also indicates a possible therapeutic role for vitamin D in preventing diabetes.
Vitamin D supplementation may reduce susceptibility to type II diabetes by slowing the loss of insulin sensitivity in people who show early signs of the disease. Researchers studied 314 adults without diabetes and gave them either 700 IU of vitamin D and 500 mg of calcium daily or a placebo for three years.73
Among subjects who had impaired (slightly elevated) fasting glucose levels at the study’s onset, those taking the active supplement had a smaller rise in glucose levels over three years than did the controls, as well as a smaller increase in insulin resistance. The researchers concluded that for older adults with impaired glucose levels, supplementing with vitamin D and calcium may help avert metabolic syndrome and type II diabetes.
Type I (insulin-dependent) diabetes is an autoimmune condition, in which the body’s immune system attacks its own insulin-producing pancreatic beta cells. Low vitamin D levels are associated with the development of autoimmune conditions,40,74,75
including type I diabetes,38
and scientists have proposed that vitamin D supplementation may help prevent the disease.76
A very large population-based study in Europe demonstrated the powerful effect of vitamin D supplementation in protecting children against the development of type I diabetes.77
Data from 820 diabetics and 2,335 non-diabetic controls showed that children who received vitamin D supplements in infancy reduced their risk of developing type I diabetes by approximately 33%. The researchers believe that activated vitamin D may protect growing children from autoimmune attack on insulin-producing cells of the pancreas.
Vitamin D May Help Alleviate Depression
It is well established that for people with major depression, symptoms tend to worsen in winter, and also that some people without baseline depression develop depressive symptoms in winter (so-called seasonal affective disorder, or SAD).94,95
Light therapy has been found to be useful for treating wintertime depressive symptoms,96
and it seems likely that at least some of the benefit of light therapy is related to increased activation of vitamin D.
To test this idea, researchers conducted a randomized trial in 15 people with SAD.95
Eight received a single dose of 100,000 IU of vitamin D, and seven received one month of light therapy. All of the supplemented patients-and none of the light-treated patients-had major improvement in depression scores. Interestingly, similar studies using much lower doses of 400-800 IU per day did not yield improvements in SAD symptoms,94,97
again suggesting that we simply need more vitamin D than has been thought.
Vitamin D’s benefits for mental health may not be limited to depression. A 2004 study from Finland98
showed that the risk of developing schizophrenia in adult men was greatly increased in those who had never had vitamin D supplementation as infants, compared to those who had had at least some supplementation. Another recent paper proposes that prenatal vitamin D deficiency could be linked to adult schizophrenia.99
Finally, a laboratory study showed that prenatal vitamin D deprivation was associated with certain behaviors in adult rats that are typical of schizophrenia in humans.100
Vitamin D Provides Essential Immune Support
Vitamin D appears to be essential in maintaining healthy white blood cells and a robust immune system.75
A recent paper presented persuasive evidence that seasonal infections such as influenza may actually be the result of decreased vitamin D levels,26
not of increased wintertime viral activity, which has been the longstanding conventional wisdom.78
This makes sense, because vitamin D receptors are present on many of the immune system cells responsible for killing viruses and deadly bacteria, and the vitamin-which is less environmentally available in the winter-appears to be a requirement for proper activation of these cells.79,80
A randomized, double-blind study published in 2006 found that vitamin D may support recovery from tuberculosis, a common and deadly infection that most commonly affects the lungs. When patients with moderately advanced tuberculosis supplemented with 0.25 mg (10,000 IU) per day of vitamin D for one week, they had significantly higher rates of improvement than patients who received a placebo.81
Kidney dialysis patients often demonstrate decreased vitamin D levels as well as impaired cellular immune response. Dialysis patients with decreased vitamin D levels and impaired function of anti-viral and anti-cancer natural killer cells experienced substantial increases in natural-killer-cell activity after just one month of supplementation with prescription vitamin D (calcitriol) at 0.5 mcg (20 IU) per day.27
In the laboratory, the same researchers demonstrated that vitamin D treatment of “generalized” white blood cells called monocytes caused them to mature into active natural killer cells within 24 hours.
Further evidence of vitamin D’s ability to bolster protective immune function comes from a laboratory study published earlier this year.82
Researchers discovered that skin cells responding to injury require vitamin D3 to “switch on” vital proteins involved in recognizing and responding to the microbes that cause wound infections. This finding has tremendous implications for preventing and treating wound infections.
Vitamin D Basics
Vitamin D occurs in nature in two main forms: vitamin D2, or ergocalciferol, and vitamin D3, or cholecalciferol. While vitamin D2 is obtained from plant sources, vitamin D3 can be either obtained through animal sources, supplements, or synthesized in the skin when its precursor molecule absorbs light energy from ultraviolet B rays.83
In the liver, both vitamin D2 and vitamin D3 are converted into 25-hydroxy-vitamin D, the primary circulating form of vitamin D. Conversion into its active form, 1,25-dihydroxyvitamin D, occurs in the kidney. Pharmaceutical drug forms of activated vitamin D include calcitriol, doxercalciferol, and calcipotriene.83
Supplemental vitamin D is available as vitamin D2 (ergocalciferol) or vitamin D3 (cholecalciferol). Vitamin D2 is only about 20-40% as effective as D3 in maintaining serum concentrations of 25-hydroxyvitamin D, since it is more rapidly broken down in the body. For this reason, vitamin D3 (cholecalciferol) supplements are considered more beneficial than vitamin D2 (ergocalciferol) supplements.7
Even in people who take vitamin D supplements, the percentage of those with sub-optimal levels remains surprisingly high. Humans cannot arbitrarily consume massive doses of vitamin D (unlike water-soluble nutrients such as vitamin C). For this nutrient, individualized dosing is of particular importance, and the only way to accomplish this is through vitamin D blood testing. With deficiencies likely to be most pronounced following the long winter months, spring is an excellent time to investigate your own vitamin D status.
Detecting deficient levels allows you and your physician to implement vitamin D supplementation to help avert illnesses associated with inadequate vitamin D levels. Optimizing your vitamin D intake may be a safe, low-cost way to protect against cardiovascular disease, diabetes, immune disorders, and depression, among other serious health conditions.
Reprinted with the kind permission of Life Extension
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