Vitamin D And Your Health
Why A 25-Hydroxyvitamin D Test May Be The Most
Important Test Your Doctor Can Give You
May 6th, 2012
By Brian Rigby, Clinical Nutrition Writer
Vitamin D is an extremely important nutrient for our bones, and is coming to be understood as vital in other areas of our body as well. Traditionally, vitamin D was not a nutrient anyone would lack, and it is not considered "essential" because our body can produce it itself.
This requires sunlight, however, which many people do not get enough of to synthesize the proper amounts of vitamin D. Without producing enough vitamin D, we begin to become deficient, and it takes a toll on our health.
Vitamin D is actually a precursor hormone, and once we either form it in our skin or ingest it, it will be converted a couple times before it reaches its final hormonal state. First, in the liver, it gets converted to a form called 25-hydroxyvitamin D, or calcidiol.
This is the form you can get tested for to detect whether you are deficient in vitamin D or not. Then, in the kidneys, it gets converted to its active form, calcitriol. Calcitriol binds to specific receptors in the body and alters gene expression, allowing vitamin D to exert its beneficial effects.
Vitamin D And Bone Health
Vitamin D is noted for its benefits to bone health more than any other effect. Through at least two mechanisms, vitamin D directly affects how strong your bones are.
Almost every nutrient we ingest gets absorbed by the small intestine through proteins called "active transporters". Active transporters are highly specific--they're like square holes, round holes, star holes, etc. You can't fit a round peg through a square hole, and calcium can't be absorbed using a sodium transporter--it can only be absorbed using calcium transporters.
The amount of calcium we absorb is limited to how many calcium transporters are active in our gut during ingestion, which is dependant on a two important things: how much calcium is in the food, and how much vitamin D is in our body. The reason vitamin D is so important is because it turns on the transporters for calcium, effectively creating more "round holes" for the calcium to go through.
This means that when vitamin D is at a proper level, much more calcium is absorbed from your food. In fact, people in a vitamin D deficient state might only absorb 10-15% of the calcium in their food, compared with 30% for people who are vitamin D sufficient!
Calcium, in addition to being an integral part of your bones, is extremely important in cellular signaling as well. For example, when your muscles contract, calcium is the 'messenger' which relays that message from your neurons to the muscle fibers. Without enough calcium in the blood, many vital functions would begin to suffer! For this reason, our body needs to keep blood calcium at a certain level, and uses another regulator of calcium to do this: the parathyroid hormone (PTH).
Whereas Vitamin D works to increase calcium available from the diet, PTH is only concerned with whether there is enough calcium in the blood for the body to function properly. If there is not enough calcium, PTH helps our body take extra calcium from the bones, increasing bone density loss. For our immediate health, having adequate levels of blood calcium is more important than having dense bones, even though the ultimate result can be bones which are brittle and easily broken.
Vitamin D works antagonistically to PTH because vitamin D keeps our blood calcium levels high from food intake, meaning PTH doesn't need to take calcium from the bones. A vitamin D deficiency can lead to a condition called secondary hyperparathyroidism, which means that too much PTH is being secreted, leading to even greater bone loss. Thus, vitamin D is crucial to the health of our bones for two closely related reasons:
1) Adequate levels of vitamin D increase the amount of calcium available from food, building bones up.
2) Inadequate levels of vitamin D increase the amount of PTH in our blood, breaking bones down.
There is also a third way in which vitamin D affects the health of our bones: VDRs are located in special bone cells called osteoblasts, and adequate vitamin D levels accelerate the formation of the bone mineral-matrix. While other factors also contribute to the formation of bones, without sufficient levels of vitamin D, the rate of bone formation is significantly decreased. This also makes vitamin D much more important in building strong bones than calcium, as no matter how much calcium you consume, it cannot accelerate the rate of bone formation like vitamin D does.
It is simplistic to reduce vitamin D to an either/or state, but that is the truth of it. All other factors aside, you can either be vitamin D sufficient, and be building bones, or you can be insufficient/deficient, and breaking bones down. There is no middle-ground.
Other Ways Vitamin D Affects Your Health
Vitamin D is no longer thought only to be important in bone health, it is now recognized as playing many roles in our body. In fact, vitamin D receptors (VDRs) are found in at least 35 different types of cells, and vitamin D can selectively activate 600-700 genes in our body, or about 3% our total number of genes! The ways in which vitamin D helps our body are not all fully understood yet, but there are a few which have been brought to light recently.
Vitamin D And Autoimmune Diseases
Vitamin D receptors are widely found in most of the immune cells our body produces, and they play a role in how our immune system responds. Of particular importance to autoimmune diseases is the way vitamin D affects immune cells called T helper cells, which have been implicated as a driving force in autoimmunity. Vitamin D reduces the T helper response, which reduces the symptoms associated with various autoimmune diseases.
More research needs to be done to determine exactly what effect vitamin D supplementation will have on autoimmune diseases such as type I diabetes, Crohn's disease, and rheumatoid arthritis, but prospective studies show that it lowers the incidence of them and may help relieve them.
Further evidence of the connection between vitamin D and autoimmune diseases is the frequency in which they occur by latitude: Incidence of certain autoimmune diseases, such as multiple sclerosis and type I diabetes, is correlated strongly with latitude, with more cases being reported in areas with less sun exposure and longer winters. While other factors may also play a role in the frequency of these diseases, it's not coincidental that many vitamin D related illnesses occur more frequently in areas with less sun exposure.
Vitamin D And Cancer
Vitamin D has been observed in numerous studies to have a protective effect against cancer, but only in patients with a sufficiently high level of vitamin D (at least 36 ng/mL). This protective effect extends to all cancers, making vitamin D one of the most potent anticarcinogenic nutrients we know of!
The mechanism through which vitamin D prevents cancer is different depending on the type of cancer, but in all cases there was a strong inverse correlation between sunshine intake/vitamin D levels and cancer incidence. For certain cancers, the reduction in rate is incredible. Studies suggest that maintaining blood levels of vitamin D above 32 ng/mL over a lifetime can reduce the risk of colorectal cancer by 50%. Similarly, maintaining levels of vitamin D above 42 ng/mL over a lifetime reduced breast cancer risk by 30%!
Vitamin D And Depression
Vitamin D deficiency has been tied to depression and other mood disorders, but more research needs to be done to understand the nature of the link. In adults suffering from depression, blood levels of vitamin D were found to be 14% lower than those not suffering from depression. In addition, levels of PTH, the hormone which is secreted in larger amounts by individuals deficient in vitamin D, were 5-33% higher depending on severity of depression, with the highest amounts being found in those with the most severe depression.
As with other markers of depression, it is not 100% clear at this point whether vitamin D deficiency leads to depression, or whether depression leads to vitamin D deficiency. In either case, obtaining sufficient levels of vitamin D could play a preventative or restorative role in our brain chemistry, as it does in adults with seasonal affective disorder (SAD).
For adults with SAD, testing has shown blood vitamin D levels to be of much more significance in improving mood than phototherapy (the use of bright lights to simulate sunlight). This suggests that the link to depressive moods in those suffering from SAD is not the amount of sunlight available, as has been theorized, but rather the amount of vitamin D available. Vitamin D may be produced in sufficient amounts during the summer months for SAD sufferers, but in some areas the winter sun is too weak to stimulate any vitamin D production, making supplementation more important than adequate light exposure in these individuals.
How Much Vitamin D Is Necessary?
Almost all research today suggests that the 400 IU recommended daily intake is simply not enough. Exactly how much people need is highly dependent on a number of external factors, such as sun exposure, skin tone, and diet, but a safe level for most individuals, absent a blood test, is 2000 IU per day. Having your healthcare practitioner perform a 25-hydroxyvitamin D test will allow you to work with them to optimize your daily intake in order to reach appropriate levels of vitamin D in your blood. For some individuals, especially during winter months, 5000 to 10,000 IU may be necessary.
What is the proper level? There is still some debate about this, but experts agree that the government's recommended levels of 20 ng/mL or above are just too low. For bone health, a minimum level of 28-32 ng/mL is recommended, but this is just the minimum. Reviewing the evidence from the studies, overall health begins to benefit at 30 ng/mL and optimal levels are between 36 and 48 ng/mL. Dr. Fuhrman recommends you get between 35 and 55 ng/mL, which is a clean, easy to remember range that will guarantee you get the most benefit out of the vitamin D without needless over-supplementing.
Vitamin D toxicity is exceedingly rare and only reported in cases of supplementation above 40,000 IU a day. The main adverse effect, short of toxicity, is hypercalcemia, or too much calcium in the blood. This, too, is rare, and suspected to only occur when blood levels of vitamin D reach 280 ng/mL or more.
This is five times the maximum blood level Dr. Fuhrman and other experts recommend! You would need to take excessive amounts of vitamin D supplements to reach 280 mg/mL, making hypercalcemia (or any other vitamin D related toxicity) an extremely unlikely occurrence. Getting a 25-hydroxyvitamin D test and working with your doctor will ensure you never reach this range. If you can't get the test, stick with 2000 IU per day.
How Can You Get Enough Vitamin D?
In times past, the best way to get vitamin D was spending a lot of time in the sun. Truly, though, those times are past as we no longer spend most of our days outdoors and shirtless. Some suggest that it only takes minutes each week to produce enough vitamin D, but a recent study done in Hawai'i found that this is not true. In the study, 51% of the participants had low vitamin D levels (less than 30 ng/mL) despite spending about four hours a day in the sun! Spending so much time in the sun unprotected has other health and cosmetic consequences, and is not a recommended method for acquiring adequate vitamin D levels, despite vitamin D being the "sunshine vitamin".
Food is also a poor source for vitamin D, unless you happen to love fish liver. Cod liver oil, the highest in vitamin D, contains a little over 1000 IU per tablespoon. Swordfish and salmon contain only about 500 IU per three ounces. Tuna has a paltry 150 IU per three ounces. To obtain sufficient vitamin D from any of these foods, aside from the cod liver oil, you would need to consume a very large amount of fish, increasing your risk of mercury poisoning.
Some processed foods and drinks are fortified with vitamin D, but they are fortified in line with the current RDA for vitamin D (400 IU). This means that most fortified foods contain only 100 IU or less, making them very poor sources of vitamin D. You would need to consume unhealthy amounts of already very unhealthy food to get sufficient vitamin D intake.
The Best Way To Get Sufficient Levels Of Vitamin D Is With Supplements
The best way to get vitamin D is from a supplement. Supplements come in precise amounts between 100 IU and 10,000 IU and above, allowing you to tailor exactly how much you need. High quality vitamin manufacturers, such as Thorne, produce vitamin D supplements without unnecessary ingredients like BHT or BHA (two preservatives which may not be labeled on commercial supplements in certain cases).
If you have not gotten a 25-hydroxyvitamin D test, or do not have the ability to get one, then 2000 IU is a good general amount to take to become vitamin D sufficient. 2000 IU is enough that most people will achieve at least 35 ng/mL, and no one runs the risk of hypercalcemia. Optimally, you should go and get tested, as 2000 IU may not be enough and there is no way to know for sure without the test.
A Vitamin D Test Is One Of The Most Important Tests You Can Get
Since vitamin D plays such a crucial role in our health, and since it is so easy to obtain sufficient levels of vitamin D through supplementation, this test may be the most important test your doctor can give you. While blood cholesterol, blood pressure, and triglyceride levels are all important in forming an overall picture of health, none of these factors alone have so broad or clear an effect on your health as vitamin D does!
Vitamin D is still relatively unstudied, but from what we have discovered, we know that it is extremely important to our body. Since vitamin D does affect so many of our genes (3% of the total!), you can expect that as more research is done, the importance of vitamin D will only grow clearer.
There are many things you should do to be healthy. Eating lots of plant-based foods, exercising, and getting enough sleep are all very important, but none are as easy to do as vitamin D supplementation is. There are no convenient foods which are high in vitamin D, and sunshine is not a guarantee of obtaining adequate levels. For these reasons, supplements are truly the way to go to be certain you get the most benefit out of vitamin D. 2000 IU a day is simple, inexpensive, and it can have dramatic effects on your health and mood!
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