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Vitamin D Toxicity:
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What Is Vitamin D?
Vitamin D is one of
the 13 known vitamins, but it's technically a hormone produced by the
body. While 11 of of the 13 vitamins are found in plant foods and can
only be taken in through our diet, D is one of the two -the other being
Vitamin
B12 - which does not conform to our traditional view of
nutrient intake.
When sunlight hits our uncovered skin, plant-derive sterols in it are converted by the ultraviolet light into Vitamin D. The vitamin then goes through processing in the liver and kidney to become physiologically active. |
For millions of years, our ancestors made their home in equatorial Africa, getting all the sunlight they needed by simply existing in their environment.
Over the course of hundreds of thousands of years, however, humans started venturing out of their homeland, heading north and south into lands where the strength of the sun varied greatly over the course of the year.
Eventually, those who settled where the sun was weak during the winter adapted to the low-light levels by losing their dark skin pigment, allowing the body to absorb as much ultraviolet light as possible. It's unclear if those in far northern and southern regions were ever able to absorb enough vitamin D for optimal health, despite their extremely white skin.
Vitamin D Toxicity: The Problem
Today, people have been
taught to fear the sun as a bringer of cancer.
Dermatologists tell them to hide their skin behind clothing and hats, slathering any exposed skin with strong sun screen lotions, which theoretically have the potential to block 95 percent of vitamin D formation when applied regularly and consistently (2).
And during the last several centuries, our civilization has changed from one where the majority people spent most of their waking hours outdoors to one where most stay indoors while the sun is out, making vitamin D production a challenge.
As our diets have worsened and the population's health has declined, maintaining vitamin D levels has become even harder than it should be under the circumstances.
Roughly a third of the U.S. population is now considered obese, with more than 70 percent considered overweight. Because vitamin D is fat soluble, excess body fat will pull vitamin D out of circulation, thus contributing to deficiency (3).
Vitamin D levels are usually measured by blood concentration. The most common suggested levels are (8):
* Insufficient 50-100 nmol/L (20-40 ng/mL)
* Mild Insufficiency 25-50 nmol/L (10-20 ng/mL)
* Moderate Insufficiency 12.5-25.0 nmol/L (5-10 ng/mL)
* Severe Insufficiency < 12.5 nmol/L (< 5 ng/mL)
However, several researchers feel that that a level of 75-80 nmol/L (30-32 ng/mL) may be sufficient (9).
Are these realistic guidelines? In my opinion, no. Even
healthy men and
women in Hawaii considered to have a large level of sun exposure
compared to the general population are unable to reach adequate D
levels under these requirements. In one study, they averaged a level of
31.6 ng/ml. The study's authors noted that 62 ng/ml was the highest
level achieved by any of the participants, which they suggested
may represent the upper healthy limit for anyone wishing to supplement
(10).
Another reason to question these guidelines is because people who don't meet them often fail to manifest any signs of deficiency.
One study of women with seasonally-adjusted vitamin D concentrations under 50 nmol/L (20 ng/ml), which would be considered deficient by standard assessments, found they had no increased risk of fractures, falls, decreased bone density, decreased grip strength, death, cardiac problems, cancer, heart failure, diabetes, high or low blood pressure, or increased weight (11).
Of course, it's entirely possible that other issues may be negatively affected, but no great measure of evidence points to this. It's also likely that, in the instance of the Hawaii study, greater levels could be achieved if they exposed themselves to the sun even more frequently than they are currently doing. It's unclear what benefits they would derive from doing so.
Vitamin D Toxicity:
It's Clear There Are Consequences
Regardless of
what an actual healthy level may be, vitamin D
deficiency is causing problems. The pharmaceutical industry has
responded by attempting to fortify food with vitamin D and by geting
people
to take supplements, a high-profit area for them.
To some degree, this has worked well. By 1920, the role Vitamin D played in preventing rickets, a scourge then affecting large parts of the United States and Europe due to the reduced amount of time people were spending in the sun, was discovered. In 1930 the U.S. government mandated milk be fortified with 10 micrograms (400 IU) of vitamin D per quart. The measure worked, and cases of rickets virtually disappeared in the country. Today, rickets are making a comeback because people are spending even less time outdoors than they were in the 1930s, leading many to call for increased food supplementation.
Many adults now suffer from osteomalacia and osteoporosis, which involve the weakening of mature bones. Both are considered directly linked to vitamin D deficiency. Other disorders where D deficiency is considered a contributing factor include cardiovascular disease, cancer, increased overall mortality risk, falls, diabetes, multiple sclerosis, osteoarthritis, epilepsy and cognitive dysfunction (9).
Unfortunately, taking isolated supplements usually proves ineffective, and in many cases dangerous.
It's the same situation here.
The largest fear with D deficiency is bone health, yet in in a 2006 review, 5 of 9 studies looking to see if supplements would reduce the risk of a hip fracture showed no decrease in breaks or overall mortality (4). Other studies have shown that the benefits for bone fracture prevention are small and largely restricted to institutionalized elderly women and, and to be effective, the studies must use a combination of vitamin D and calcium, not vitamin D alone (5,7).
Even though there is an association between lower vitamin D levels and increased risk of heart disease, strokes, type-2 diabetes, multiple sclerosis, as well as breast, prostate, and colon cancer, supplements have not been shown to be effective for these conditions (5-7).
The evidence that D supplements are not preventing or correcting the problems caused by D deficiency has grown so strong that the medical opinion in favor of them is changing.
In the March 2010 issue of the Annals of Internal Medicine, the editorial concludes: "Despite the promise for disease prevention suggested by available studies, we believe that the evidence for widespread use of high-dose vitamin D supplementation in the general population remains insufficient."
What researchers are finding is that supplementation easily raises the level of vitamin D in the blood, but that this doesn't seem to actually prevent disease.
Unlike vitamin B12, which the body cannot overdose on, there may be significant health consequences that result from supplementing vitamin D: vitamin D toxicity.
It's long been known that adults develop vitamin D toxicity (Hypervitaminosis D) after several months of taking supplements of 1250 micrograms/day (50,000 IU). More recently, smaller doses are even being reconsidered because even they might introduce vitamin D toxicity and the attendent health problems.
A number of recent studies have shown that at dosages considered safe (generally around 300-400 IU/day), increases in LDL-cholesterol, prostate cancer, immune system suppression, autoimmune diseases, gastrointestinal symptoms, kidney disease, and calcium stones has been observed caused by D supplements (13-19).
Whether or not this is recognized as vitamin D toxicity, there appears to be some significant health consequences on the line.
Vitamin D Toxicity:
Because it appears that deficiency brings on disease but supplementation is ineffective at best and possibly harmful, we're left in a real bind. Damned if you do and damned if you don't? Not quite.
Just like people are looking for quick shortcuts to a healthy body, fitness, and weight loss, people want the quick fix for the D deficiency. It's much easier to pop a pill than to actually adjust your lifestyle to make yourself healthier.
It's no surprise that people who have higher vitamin D levels happen to be comparatively thin, exercise, eat a relatively good diet, and generally follow a healthy lifestyle (20).
Similarly, those who have lower levels of vitamin D tend to smoke, have a parental history of heart attack (which often indicates that the family norms passed on through generations include a high-fat diet), drink alcohol regularly, and suffer from chronic illnesses (20).
As mentioned previously, overweight people are also much
more likely to
have a deficiency, and considering that most of the population of
western countries is overweight, this is a big contributing factor.
Researchers often note that those who have low D levels have an increased risk of disease, and although this is probably very true, the poor lifestlye that kept them out of the sun probably contributed to their ill health.
The only safe course is to start changing your life to pursue health.
Vitamin D Toxicity:
There's no question that the sun exerts an incredibly positive influence on us, helping our mind, cleansing out skin, and likely providing us with aid that science does not yet understand.
In my ebook, The Raw Food Lifestyle, I talk about how the sun has successfully been used to assist the body in healing itself in a number of ways, and give suggestions for incorporating more of it into your life, no matter what climate you live in.
I feel that it is the only safe way to provide ourselves with D.
Unlike supplement intake, it's virtually impossible to achieve vitamin D toxicity through sun exposure under most circumstances (21). This is because within about 20 minutes of ultraviolet exposure in light-skinned individuals (or 3–6 times longer for darker-skinned people) the concentrations of vitamin D precursors produced in the skin reach an equilibrium, and any further vitamin D that is produced is degraded (22).
The amount of vitamin D produced through sun exposure at the point that the skin becomes slightly red has been estimated at 10,000 IU per day (21), however, it's not clear how much of this is absorbed by the body.
Vitamin D Toxicity:
People want to believe there must be a easy solution to this problem. The fact remains that our species originated in the tropics, and leaving them behind has degraded out health in a number of ways. It's possible that living in the far north or south is inherently unhealthy due to the lack of sun, and nothing we can do will make up for it.
Supplements
won't
do
it,
although you will continue to see them vigerously
promoted, despite what science may have to say about it, because they
are extremely lucrative.
What about tanning beds? They generate vitamin D on the skin, but they do not replicate the sun's rays, and it's hard to say how they might affect us. Even so, I'd probably consider a tanning bed before supplementing because it at least replicates the basic process of generating D on the skin.
At the end of the day, we're back to the healthy living. Will you live a healthy life? Will you keep your body fat levels low, eat a raw vegan diet, exercise regularly, and otherwise create a good lifestyle? If you do these things, your ability to deal with a any single deficiency is increased.
And if if you're unhappy about the amount of sunshine your home gets, maybe it's time to consider a move.
Enjoy the sun :)
Dermatologists tell them to hide their skin behind clothing and hats, slathering any exposed skin with strong sun screen lotions, which theoretically have the potential to block 95 percent of vitamin D formation when applied regularly and consistently (2).
And during the last several centuries, our civilization has changed from one where the majority people spent most of their waking hours outdoors to one where most stay indoors while the sun is out, making vitamin D production a challenge.
As our diets have worsened and the population's health has declined, maintaining vitamin D levels has become even harder than it should be under the circumstances.
Roughly a third of the U.S. population is now considered obese, with more than 70 percent considered overweight. Because vitamin D is fat soluble, excess body fat will pull vitamin D out of circulation, thus contributing to deficiency (3).
Vitamin D Toxicity: How Much Do We Need?
How much vitamin D we need
has long been a matter of contention, and because it's clear that
taking too much causes vitamin D toxicity, and because these guidelines
are used to
judge who is deficient, it's an important question.
Vitamin D levels are usually measured by blood concentration. The most common suggested levels are (8):
* Insufficient 50-100 nmol/L (20-40 ng/mL)
* Mild Insufficiency 25-50 nmol/L (10-20 ng/mL)
* Moderate Insufficiency 12.5-25.0 nmol/L (5-10 ng/mL)
* Severe Insufficiency < 12.5 nmol/L (< 5 ng/mL)
However, several researchers feel that that a level of 75-80 nmol/L (30-32 ng/mL) may be sufficient (9).
Are these realistic guidelines? In my opinion, no. Even
healthy men and
women in Hawaii considered to have a large level of sun exposure
compared to the general population are unable to reach adequate D
levels under these requirements. In one study, they averaged a level of
31.6 ng/ml. The study's authors noted that 62 ng/ml was the highest
level achieved by any of the participants, which they suggested
may represent the upper healthy limit for anyone wishing to supplement
(10). Another reason to question these guidelines is because people who don't meet them often fail to manifest any signs of deficiency.
One study of women with seasonally-adjusted vitamin D concentrations under 50 nmol/L (20 ng/ml), which would be considered deficient by standard assessments, found they had no increased risk of fractures, falls, decreased bone density, decreased grip strength, death, cardiac problems, cancer, heart failure, diabetes, high or low blood pressure, or increased weight (11).
Of course, it's entirely possible that other issues may be negatively affected, but no great measure of evidence points to this. It's also likely that, in the instance of the Hawaii study, greater levels could be achieved if they exposed themselves to the sun even more frequently than they are currently doing. It's unclear what benefits they would derive from doing so.
Vitamin D Toxicity:
It's Clear There Are Consequences
Regardless of
what an actual healthy level may be, vitamin D
deficiency is causing problems. The pharmaceutical industry has
responded by attempting to fortify food with vitamin D and by geting
people
to take supplements, a high-profit area for them. To some degree, this has worked well. By 1920, the role Vitamin D played in preventing rickets, a scourge then affecting large parts of the United States and Europe due to the reduced amount of time people were spending in the sun, was discovered. In 1930 the U.S. government mandated milk be fortified with 10 micrograms (400 IU) of vitamin D per quart. The measure worked, and cases of rickets virtually disappeared in the country. Today, rickets are making a comeback because people are spending even less time outdoors than they were in the 1930s, leading many to call for increased food supplementation.
Many adults now suffer from osteomalacia and osteoporosis, which involve the weakening of mature bones. Both are considered directly linked to vitamin D deficiency. Other disorders where D deficiency is considered a contributing factor include cardiovascular disease, cancer, increased overall mortality risk, falls, diabetes, multiple sclerosis, osteoarthritis, epilepsy and cognitive dysfunction (9).
Vitamin D Toxicity: Supplements Won't Cut It
Unfortunately, taking isolated supplements usually proves ineffective, and in many cases dangerous.
It's the same situation here.
The largest fear with D deficiency is bone health, yet in in a 2006 review, 5 of 9 studies looking to see if supplements would reduce the risk of a hip fracture showed no decrease in breaks or overall mortality (4). Other studies have shown that the benefits for bone fracture prevention are small and largely restricted to institutionalized elderly women and, and to be effective, the studies must use a combination of vitamin D and calcium, not vitamin D alone (5,7).
Even though there is an association between lower vitamin D levels and increased risk of heart disease, strokes, type-2 diabetes, multiple sclerosis, as well as breast, prostate, and colon cancer, supplements have not been shown to be effective for these conditions (5-7).
The evidence that D supplements are not preventing or correcting the problems caused by D deficiency has grown so strong that the medical opinion in favor of them is changing.
In the March 2010 issue of the Annals of Internal Medicine, the editorial concludes: "Despite the promise for disease prevention suggested by available studies, we believe that the evidence for widespread use of high-dose vitamin D supplementation in the general population remains insufficient."
What researchers are finding is that supplementation easily raises the level of vitamin D in the blood, but that this doesn't seem to actually prevent disease.
Vitamin D Toxicity: Supplementing Can Harm You
Unlike vitamin B12, which the body cannot overdose on, there may be significant health consequences that result from supplementing vitamin D: vitamin D toxicity.
It's long been known that adults develop vitamin D toxicity (Hypervitaminosis D) after several months of taking supplements of 1250 micrograms/day (50,000 IU). More recently, smaller doses are even being reconsidered because even they might introduce vitamin D toxicity and the attendent health problems.
A number of recent studies have shown that at dosages considered safe (generally around 300-400 IU/day), increases in LDL-cholesterol, prostate cancer, immune system suppression, autoimmune diseases, gastrointestinal symptoms, kidney disease, and calcium stones has been observed caused by D supplements (13-19).
Whether or not this is recognized as vitamin D toxicity, there appears to be some significant health consequences on the line.
Vitamin D Toxicity:
Then What Should We Do?
Because it appears that deficiency brings on disease but supplementation is ineffective at best and possibly harmful, we're left in a real bind. Damned if you do and damned if you don't? Not quite.
Just like people are looking for quick shortcuts to a healthy body, fitness, and weight loss, people want the quick fix for the D deficiency. It's much easier to pop a pill than to actually adjust your lifestyle to make yourself healthier.
It's no surprise that people who have higher vitamin D levels happen to be comparatively thin, exercise, eat a relatively good diet, and generally follow a healthy lifestyle (20).
Similarly, those who have lower levels of vitamin D tend to smoke, have a parental history of heart attack (which often indicates that the family norms passed on through generations include a high-fat diet), drink alcohol regularly, and suffer from chronic illnesses (20).
As mentioned previously, overweight people are also much
more likely to
have a deficiency, and considering that most of the population of
western countries is overweight, this is a big contributing factor. Researchers often note that those who have low D levels have an increased risk of disease, and although this is probably very true, the poor lifestlye that kept them out of the sun probably contributed to their ill health.
The only safe course is to start changing your life to pursue health.
Vitamin D Toxicity:
The Power Of The Sun
There's no question that the sun exerts an incredibly positive influence on us, helping our mind, cleansing out skin, and likely providing us with aid that science does not yet understand.
In my ebook, The Raw Food Lifestyle, I talk about how the sun has successfully been used to assist the body in healing itself in a number of ways, and give suggestions for incorporating more of it into your life, no matter what climate you live in.
I feel that it is the only safe way to provide ourselves with D.
Unlike supplement intake, it's virtually impossible to achieve vitamin D toxicity through sun exposure under most circumstances (21). This is because within about 20 minutes of ultraviolet exposure in light-skinned individuals (or 3–6 times longer for darker-skinned people) the concentrations of vitamin D precursors produced in the skin reach an equilibrium, and any further vitamin D that is produced is degraded (22).
The amount of vitamin D produced through sun exposure at the point that the skin becomes slightly red has been estimated at 10,000 IU per day (21), however, it's not clear how much of this is absorbed by the body.
Vitamin D Toxicity: But I Live In A Far Northern or Far Southern Environment
I live in Connecticut, where
it's likely impossible to generate vitamin D during much of the
winter,
although this is not absolutely certain. Many other are in similar
binds.
Vitamin D is fat soluble, and if you build up a good store it it, your body will release it over the course of the winter, though in lower quantities and quality than D generated by recent sun exposure.
How much D you have circulating during the winter is determined by how much you produce during the spring, summer, and fall. For instance, you need to achieve a blood concentration of 40 nmol/I during the sunnier months to achieve a winter circulation of 15-22.5 nmol/l (23).
How long do our reserves last? By testing people stuck on military submarines, where they can get no sun, researchers have determined that it takes two months without sun to reach half-life, that state of having our reserves reduced by half (24).
Generally, researchers believe a person can generate vitamin D year-round in the area of land south of 37 degrees north and north of 37 degrees south. In the United States, 37 degrees north runs close to Richmond Virginia on the east coast and Sanfransico on the west coast.
The farther outside of this band you get, the longer the period of time during the winter when you can get no vitamin D. In Boston, for instance it's believed that no vitamin D can be generated from late October to early March. Wherever these periods last for four or more months, it's possible that you will become deficient. People living in these regions are more likely to be deficient than those living closer to the equator, but the point to take home is that not all of them are.
But even living in a sunny environment is no guarantee. Because people don't venture outside much, even Australia, which gets tons of sunshine by American standards, has a large D deficiency problem (9).
It's truly up to you to take the right steps and ensure you expose yourself to the sun.
Vitamin D is fat soluble, and if you build up a good store it it, your body will release it over the course of the winter, though in lower quantities and quality than D generated by recent sun exposure.
How much D you have circulating during the winter is determined by how much you produce during the spring, summer, and fall. For instance, you need to achieve a blood concentration of 40 nmol/I during the sunnier months to achieve a winter circulation of 15-22.5 nmol/l (23).
How long do our reserves last? By testing people stuck on military submarines, where they can get no sun, researchers have determined that it takes two months without sun to reach half-life, that state of having our reserves reduced by half (24).
Generally, researchers believe a person can generate vitamin D year-round in the area of land south of 37 degrees north and north of 37 degrees south. In the United States, 37 degrees north runs close to Richmond Virginia on the east coast and Sanfransico on the west coast.
The farther outside of this band you get, the longer the period of time during the winter when you can get no vitamin D. In Boston, for instance it's believed that no vitamin D can be generated from late October to early March. Wherever these periods last for four or more months, it's possible that you will become deficient. People living in these regions are more likely to be deficient than those living closer to the equator, but the point to take home is that not all of them are.
But even living in a sunny environment is no guarantee. Because people don't venture outside much, even Australia, which gets tons of sunshine by American standards, has a large D deficiency problem (9).
It's truly up to you to take the right steps and ensure you expose yourself to the sun.
Vitamin D Toxicity: Steps You Can Take
- The root cause of all vitamin D deficiency is a lack
of sun exposure. First, stop hiding from the sun and slathering on sun
screen. You don't have to worry about achieving vitamin D toxicity from
sun exposure. Simply don't allow yourself to get burnt, but gradually
build up a tan
for exposing yourself more and more each day. In most of the United
States you can generate D for three-quarters of the year. A low-fat
diet with tons of fruits and vegetables can help you not burn.
- If you live beyond 37 degrees, the easiest way to sidestep deficiency is to take a vacation to the tropics in the middle of winter. A week of sunshine will restore your reserves and get you through to spring.
- If you cannot take a vacation but have wisely exposed
yourself to the sun every day during the spring, summer, and fall, it's
probable that you can make it through a three or four-month "vitamin D
winter" without any problems. Beyond this, you're likely in trouble.
- When exposing yourself to the sun, don't listen to
the experts, who may suggest 5-10 minutes is sufficient. Realize that
those with darker skin pigments need much more than this, and that even
very white-skinned people develop tans that cut down on how quickly
they create D as they expose themselves. The key is never let yourself
burn. If you're not burning, you're not overdoing it.
- Although there is no science to back it up, there may
be benefits to be derived from exposing as much of your body to the sun
as you can during the winter. I do this and feel that I benefit from
it. On
a sunny day in winter, running in a short-sleeved shirt is not
unpleasant.
Vitamin D Toxicity:
There May Be No Easy Answer
People want to believe there must be a easy solution to this problem. The fact remains that our species originated in the tropics, and leaving them behind has degraded out health in a number of ways. It's possible that living in the far north or south is inherently unhealthy due to the lack of sun, and nothing we can do will make up for it.
Supplements
won't
do
it,
although you will continue to see them vigerously
promoted, despite what science may have to say about it, because they
are extremely lucrative. What about tanning beds? They generate vitamin D on the skin, but they do not replicate the sun's rays, and it's hard to say how they might affect us. Even so, I'd probably consider a tanning bed before supplementing because it at least replicates the basic process of generating D on the skin.
At the end of the day, we're back to the healthy living. Will you live a healthy life? Will you keep your body fat levels low, eat a raw vegan diet, exercise regularly, and otherwise create a good lifestyle? If you do these things, your ability to deal with a any single deficiency is increased.
And if if you're unhappy about the amount of sunshine your home gets, maybe it's time to consider a move.
Enjoy the sun :)
Vitamin D
Toxicity:
Following Up
Learn more about the health-giving properties of the sun and how you incorporate more of it into your life in The Raw Food Lifestyle.
Avoid vitamin D toxicity and adopt a healthy raw food diet that will put you on a path toward health.
Find out more about our nutritional needs here.
Vitamin D Toxicity: Sources
1) Holick MF. Vitamin D deficiency. N Engl J Med. 2007;357(3):266-281.
2) Sayre RM, Dowdy JC (2007). "Darkness at noon: sunscreens and vitamin D3". Photochemistry and Photobiology 83 (2): 459–63. doi:10.1562/2006-06-29-RC-956 (inactive 2010-01-07). PMID 17115796.
3) Smotkin-Tangorra M, Purushothaman R, Gupta A, Nejati G, Anhalt H, Ten S. Prevalence of vitamin D insufficiency in obese children and adolescents. J Pediatr Endocrinol Metab. 2007 Jul;20(7):817-23.
4) Wolpowitz D, Gilchrest BA. The vitamin D questions: how much do you need and how should you get it? J Am Acad Dermatol. 2006 Feb;54(2):301-17.
5) Pittas AG, Chung M, Trikalinos T, Mitri J, Brendel M, Patel K, Lichtenstein AH, Lau J, Balk EM. Systematic review: Vitamin D and cardiometabolic outcomes. Ann Intern Med. 2010 Mar 2;152(5):307-14
6) Wang L, Manson JE, Song Y, Sesso HD. Systematic review: Vitamin D and calcium supplementation in prevention of cardiovascular events. Ann Intern Med. 2010 Mar 2;152(5):315-23.
7) Grey A, Bolland MJ, Reid IR. Vitamin D supplementation. Arch Intern Med. 2010 Mar 22;170(6):572-3
8) Stroud ML, Stilgoe S, Stott VE, Alhabian O, Salman K (December 2008). "Vitamin D — a review". Australian Family Physician 37 (12): 1002–5. PMID 19142273. http://www.racgp.org.au/afp/200812/29319.
9) Joshi, D; Center, J; Eisman, J (2010). "Vitamin D deficiency in adults". Australian Prescriber (33): 103–6.
10) Binkley, N.; Novotny, R.; Krueger, D.; Kawahara, T.; Daida, Y.; Lensmeyer, G.; Hollis, B.; Drezner, M. (2007). "Low vitamin D status despite abundant sun exposure". The Journal of clinical endocrinology and metabolism 92 (6): 2130–2135. doi:10.1210/jc.2006-2250. PMID 17426097.
11) Bolland, M.; Bacon, C.; Horne, A.; Mason, B.; Ames, R.; Wang, T.; Grey, A.; Gamble, G. et al. (2010). "Vitamin D insufficiency and health outcomes over 5 y in older women.". The American journal of clinical nutrition 91 (1): 82–89. doi:10.3945/ajcn.2009.28424. PMID 1990679
12) Holick MF (December 2004). "Sunlight and vitamin D for bone health and prevention of autoimmune diseases, cancers, and cardiovascular disease". The American Journal of Clinical Nutrition 80 (6 Suppl): 1678S–88S. PMID 15585788.
13) Heikkinen AM, Tuppurainen MT, Niskanen L, Komulainen M, Penttil I, Saarikoski S. Long-term vitamin D3 supplementation may have adverse effects on serum lipids during postmenopausal hormone replacement therapy. Eur J Endocrinol. 1997 Nov;137(5):495-502.
14) Tuppurainen M, Heikkinen AM, Penttil I, Saarikoski S. Does vitamin D3 have negative effects on serum levels of lipids? A follow-up study with a sequential combination of estradiol valerate and cyproterone acetate and/or vitamin D3. Maturitas. 1995 Jun;22(1):55-61.15) Witham MD. Vitamin D deficiency: More evidence is needed before general supplementation. BMJ. 2008 Jun 28;336(7659):1451
16) Tuohimaa P, Tenkanen L, Ahonen M, Lumme S, Jellum E, Hallmans G, Stattin P, Harvei S, Hakulinen T, Luostarinen T, Dillner . Both high and low levels of blood vitamin D are associated with a higher prostate cancer risk: a longitudinal, nested case-control study in the Nordic countries. Int J Cancer. 2004 Jan 1;108(1):104-8.
17) Marshall TG. Vitamin D discovery outpaces FDA decision making. Bioessays. 2008 Feb;30(2):173-82.
18) Meyer G, Kpke S. Vitamin D and falls. Information on harm is missing. BMJ. 2009 Oct 28;339:b4395. doi: 10.1136/bmj.b4395.
19) Hsia J, Heiss G, Ren H, Allison M, Dolan NC, Greenland P, et al. 2007 Women's Health Initiative. Calcium/ vitamin D supplementation and cardiovascular events. Circulation 2007;115:846-54.
(20) Pittas AG, Chung M, Trikalinos T, Mitri J, Brendel M, Patel K, Lichtenstein AH, Lau J, Balk EM. Systematic review: Vitamin D and cardiometabolic outcomes. Ann Intern Med. 2010 Mar 2;152(5):307-14
(21) Vieth R (May 1999). "Vitamin D supplementation, 25-hydroxyvitamin D concentrations, and safety". The American Journal of Clinical Nutrition 69 (5): 842–56. PMID 10232622.
(22) Holick MF (March 1995). "Environmental factors that influence the cutaneous production of vitamin D". The American Journal of Clinical Nutrition 61 (3 Suppl): 638S–645S. PMID 7879731.
23) Relative contributions of diet and sunlight to vitamin D state in the elderly. Lawson DE, Paul AA, Black AE, Cole TJ, Mandal AR, Davie M. Br Med J. 1979 Aug 4;2(6185):303-5.
24) Vieth R. What is the optimal vitamin D status for health? Prog Biophys Mol Biol. 2006 Sep;92(1):26-32.
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