What can high-vitamin D foods do for you?
- Help prevent a growing list of chronic diseases, including type 2 diabetes, heart disease, hypertension, osteoporosis, breast cancer, colon cancer, and ovarian cancer
- Help keep your bones and teeth strong and healthy
- Regulate the growth and activity of your cells
- Reduce inflammation
What events can indicate a need for more foods rich in vitamin D?
- Bone pain and/or soft bones
- Frequent bone fractures
- Bone deformities or growth retardation in children
- Lack of exposure to sunlight for any reason, including geography, use of sunscreen, or wearing of protective clothing
Concentrated food sources of vitamin D include salmon, sardines, shrimp, milk, cod, and eggs.
Sockeye salmon are an exceptionally rich source of vitamin D: a 4-ounce serving of baked or broiled sockeye salmon provides 739.37 IU of vitamin D. The same 4-ounce serving of chinook salmon, another excellent source of vitamin D, supplies 411 IU.
Why are sockeye salmon even more richly endowed with vitamin D than other salmon species? Because zooplankton constitutes so much of their diet, and zooplankton-along with phytoplankton-are the key sources of vitamin D in the marine food chain. The zooplankton eaten by salmon are tiny marine animals, such as larval-stage crustaceans, while the phytoplankton eaten by salmon are small, plant-like marine organisms.
Both types of minuscule sea life create lots of vitamin D from sunlight, and zooplankton feed on phytoplankton, building up their vitamin D content to even higher levels. Unlike most other fish and salmon species (except chum), sockeye feed largely on zooplankton through all stages of life. Chinook, on the other hand, feast on insects and side swimmers when young, then consume a variety of fish, especially smelt and ciscoes, a type of lake herring, as they mature.
Early in the 20th century scientists discovered that rickets, a childhood disease characterized by improper bone development, could be prevented by a compound isolated from cod liver oil referred to as "fat-soluble factor D," now known as vitamin D. The vitamin was also called "calciferol," since it was found to boost calcium deposits in bone. Because vitamin D is so important in skeletal growth and strong bones, many foods are fortified with this vitamin to ensure that children obtain adequate amounts.
There are two basic types of vitamin D. Ergosterol is the basic building block of vitamin D in plants. Cholesterol is the basic building block of vitamin D in humans. When ultraviolet light from the sun hits the leaf of a plant, ergosterol is converted into ergocalciferol, or vitamin D2. In just the same way, when ultraviolet light hits the cells of our skin, one form of cholesterol found in our skin cells - called 7-dehydrocholesterol - can be converted into cholecalciferol, a form of vitamin D3.
In the life of a plant, the ergocalciferol form of vitamin D2 serves to accomplish most of the desired purposes that were intended for this substance. In the life of a human, however, cholecalciferol is not the final intended form for this vitamin. In order for our bodies to come up with the fully active form of vitamin D3, further metabolism is required in our liver and our kidneys. This additional metabolism takes the cholecalciferol form of vitamin D3 and converts it into a fully active form (called 1,25-dihydroxycholecalciferol, or simply "calcitriol"). Because cholecalciferol does not qualify as the fully active form of vitamin D3 in humans, it is often referred to as "provitamin D" (or "provitamin D3"). The "pro" in this word "provitamin" means the same thing as "preliminary form."
While plants typically stop at ergocalciferol in their own metabolism of vitamin D2, humans who consume vitamin D2 in plant form can take the ergocalciferol and convert it (once again using the liver and the kidneys) into 1,25-dihydroxyergocalciferol, or ercalcitriol. In the past, these two forms of vitamin D (calcitriol originating in animals, and ercalcitriol originating in plants) - were not carefully differentiated in research studies or in the manufacture of vitamin D supplements. More recently, however, we believe that ercalcitriol has clearly been shown to be an inferior form of vitamin D when it comes to vitamin supplements. If you are an individual who takes vitamin D supplements, and you prefer plant sources of nutrients in your supplements, you may want to consult with your healthcare practitioner when deciding about the best option in your individual circumstances. Many animal-based vitamin D supplements containing cholecalciferol are derived from 7-dehydrocholesterol that was produced by the sebaceous glands in the skin of an animal (typically sheep) and then removed from the fur of the animal (typically raw sheep's wool), and exposed to UVB (ultra-violet B) light that converts it into cholecalciferol.
Maintaining proper calcium levels in the blood
Although typically categorized as a fat-soluble vitamin, vitamin D actually functions more like a hormone. Calcitriol, the most metabolically active form of vitamin D, works with parathyroid hormone (PTH) to maintain proper levels of calcium in the blood. Low levels of calcium in the blood stimulate the secretion of PTH from the parathyroid gland. PTH then stimulates the conversion of inactive forms of vitamin D to calcitriol. Calcitriol acts to increase the intestinal absorption of calcium, increase the resorption of calcium by the kidneys, and stimulate the release of calcium from the bone, thereby increasing blood calcium levels. Alternatively, when blood levels of calcium are too high, calcitriol decreases the intestinal absorption of calcium and stimulates the bones to take up calcium, thereby decreasing blood calcium levels.
Maintaining proper phosphorus levels in the blood
When vitamin D levels remain problematically low, the parathyroid gland becomes overactive, a condition known as hyperparathyroidism. PTH levels rise, and blood levels of phosphorus drop. Without adequate phosphorus, bone cannot be properly mineralized, which contributes to the defects seen in osteomalacia. In addition, the new bone cells being laid down by the osteoblasts (the cells that create new bone) absorb more water and swell, causing the bone pain associated with osteomalacia.
Maintaining normal cellular growth and function
Scientists have recently discovered that our bodies convert vitamin D3 into calcitriol not only in the kidneys but in other tissues as well, including the lymph glands and skin. Because calcitriol is so closely involved with the lifecycles of our cells, this discovery has led scientists to believe that vitamin D may be very important in the prevention and treatment of certain cancers.
Vitamin D may also play a role in regulating cellular growth and function in our brain cells. In mice studies, vitamin D has been found to have a significant effect on brain cell (neuronal) growth and division. The brains of vitamin D deficient rats look different. If vitamin D is not present during gestation, long-lasting defects occur. Future research may well determine that development of the human brain is also closely tied to our vitamin D status.
Maintaining healthy immune function and preventing excessive inflammation
Vitamin D also helps regulate immune system activity, preventing an excessive or prolonged inflammatory response. Our immune cells, specifically our active T-cells, have receptors for vitamin D. This is important because autoimmune diseases-including multiple sclerosis, diabetes, rheumatoid arthritis, irritable bowel diseases (such as Crohn's and ulcerative colitis-all have a T-cell component of inflammation.
For example, in multiple sclerosis, T helper cells drive the progression of the disease by recruiting other inflammatory immune cells (macrophages and inflammatory cytokines)-particularly when vitamin D is deficient. When vitamin D levels are adequate, the body switches on a vitamin-D mediated system that can help shut down the inflammation.
Periodontal disease, a chronic inflammatory gum disease common in those over 50, is another example of a lack of vitamin D resulting in a progressive, inflammatory condition. A study published in the American Journal of Clinical Nutrition (July 2004) that evaluated 11,202 subjects 20 years of age or older found that, in both men and women over 50, lack of vitamin D significantly increased risk of periodontal disease. Men with the lowest blood levels of vitamin D had a 61% higher risk of periodontal disease than men with the highest levels. Women with the least vitamin D in their blood had an even higher, 74% increased risk of periodontal disease. In men and women younger than 50, no significant association between vitamin D levels and periodontal disease was found. The take-home message from this study: if you're over 50, particularly if you live in northern latitudes or slather on the sunscreen to protect your skin from age spots or skin cancer, be sure to make vitamin D-rich foods staples in your healthy way of eating.
Vitamin D's anti-inflammatory effects are seen across a wide spectrum of health conditions including hypertension, type 1 diabetes, and psoriasis.
High blood pressure has been correlated with living at higher latitudes, and, by implication, insufficient vitamin D levels. In a group of individuals with high blood pressure, those whose UVB exposure was increased by using tanning beds (30 min/3 times a week) increased their vitamin D levels by 180% and decreased their blood pressure by about 5%.
Vitamin D deficiency has also been associated with heart failure in humans. One possible mechanism involves the relationship between vitamin D and renin levels, since renin, an enzyme secreted by the kidney, is important in the regulation of blood pressure and heart health.
Vitamin D deficiency accelerates progression to type 1 diabetes in diabetic-prone mice, but if they are given Vitamin D3, their risk of progression drops by 80%. Whether this relationship holds true for humans has yet to be determined.
An inverse relationship has also been noted between type 1 diabetes mellitus and increased latitude.
Children in Finland getting 2,000 IU vitamin D/day through dietary supplements were found to have reduced their risk of type 1 diabetes mellitus by 80%! Conversely, children deficient in vitamin D were found to have a 4-fold increased risk of developing type 1 diabetes.
Since the vitamin D receptor is present in the skin, one of the foremost researchers in the area of vitamin D studies, Dr. Michael Holick, MD, Ph.D., postulated that a cream containing activated vitamin D might be helpful in the treatment of psoriasis and developed a cream to use. As Director of the Vitamin D Research Lab at Boston University Medical Center, Dr. Holick has now treated 1,000+ individuals with psoriasis, and although only a pilot study has been published as of 2005, about 92% improve with topical application of activated vitamin D.
Vitamin D deficiency has also been associated with an increased risk of certain cancers. These cancers include breast cancer, colon cancer, and ovarian cancer.
What are deficiency symptoms for vitamin D?
Vitamin D deficiency results in decreased absorption of calcium and phosphorus. As a result, prolonged vitamin D deficiency has a negative impact on bone mineralization. In infants and children, such a deficiency manifests itself as rickets, a condition characterized by bone deformities and growth retardation. Adults with vitamin D deficiency may experience bone pain and/or osteomalacia (soft bone).
It is particularly important for individuals with limited sun exposure to include good sources of vitamin D in their diets. Homebound individuals, people living in northern latitudes, individuals who wear clothing that completely covers the body, and individuals working in occupations that prevent exposure to sunlight are at risk for vitamin D deficiency.
In addition, breast milk may not contain a sufficient amount of vitamin D, so exclusively breast-fed infants may require supplemental vitamin D.
What are toxicity symptoms for vitamin D?
Excessive dietary intake of vitamin D can be toxic. Toxicity of vitamin D can come from either its plant-based (D2) or animal-based (D3) form. Symptoms of toxicity include loss of appetite, nausea, vomiting, high blood pressure, kidney malfunction, and failure to thrive.
In 1997, the National Academy of Sciences set Tolerable Upper Intake Levels (ULs) for vitamin D as follows: infants, 0-12 months, 25 micrograms (1,000 IU) per day; children and adults, 50 micrograms (2,000 IU) per day; pregnant and lactating women, 50 micrograms (2,000 IU) per day.
Individuals with hyperparathyroidism, overactivity of the parathyroid gland, are at increased risk for vitamin D toxicity, and should not take supplemental vitamin D without consulting a physician.
How do cooking, storage, or processing affect vitamin D?
Vitamin D is a stable compound. Neither cooking nor long-term storage significantly reduce vitamin D levels in food.
What factors might contribute to a deficiency of vitamin D?
Insufficient sun exposure
It is especially important for individuals with limited sun exposure to include good sources of vitamin D in their diets. Homebound individuals, people living in northern latitudes, individuals who wear clothing that completely covers the body, and individuals who always use sunscreen or work in occupations that prevent exposure to sunlight are at significant risk for vitamin D deficiency.
In northern latitudes (above 51° latitude), in spring, summer, and fall, we can make vitamin D from exposure to sunlight (15 minutes, 2-3 times per week is all that is needed), but in the winter we cannot make any. Below 35° latitude, vitamin D can be made year-round. But at higher and higher latitudes, our ability to make vitamin D gets more and more seasonally limited. At about 51° latitude, we may go 3 months without being able to make vitamin D. At about 71° latitude we may go more than 5 months.
African Americans need significantly more UV exposure to produce adequate vitamin D. This is because darker skin contains more melanin, the pigment that gives skin its color, and the higher melanin content in darker skin reduces the skin's ability to produce vitamin D from sunlight. Throughout the U.S., as many as 30-50% of African Americans may be vitamin D deficient.
Breastfeeding, if the mother is vitamin D deficient
If a mother is deficient in vitamin D and her infant is exclusively breast-fed, that infant may require a vitamin D supplement in order to avoid vitamin D deficiency.
Obesity is also associated with vitamin D deficiency. Since vitamin D is fat-soluble, it can be taken into fat cells and stored, thus making it potentially less available in our body's metabolism. Production of vitamin D may also be reduced in obese individuals. For example, in one study, when normal and obese subjects were exposed to the same amount of radiation from natural sunlight, obese subjects only produced 55% the amount of vitamin D as normal-weight subjects.
Insufficient dietary fat or inability to absorb dietary fat
Since vitamin D is a fat-soluble vitamin, a diet that is extremely low in fat, and/or the presence of certain medical conditions that cause a reduction in the ability to absorb dietary fat, may cause vitamin D deficiency.
These medical conditions include pancreatic enzyme deficiency, Crohn's disease, celiac sprue, cystic fibrosis, surgical removal of part or all of the stomach, gall bladder disease, and liver disease. Symptoms of fat malabsorption include diarrhea and greasy stools.
Health conditions that involve the parathyroid gland or kidney
Under certain circumstances, the conversion of inactive forms of vitamin D to calcitriol is impaired. For example, diseases that affect the parathyroid gland, liver and/or kidney impair the synthesis of the active form of vitamin D.
The production of vitamin D precursors in the skin decreases with age, and the kidney is less able to convert vitamin D to its active hormone form.
Some individual's genetic inheritance includes genetic polymorphisms that result in the production of vitamin D receptors (VDR) that don't work very well. To help compensate for such VDR defects, these individuals need more vitamin D than would normally be necessary.
What medications affect vitamin D?
The following medications impact the absorption, utilization and/or activation of vitamin D:
- Anticonvulsant medications, including Dilantin, are used to control seizure activity in people with epilepsy and brain cancer, and those who have suffered head trauma through injury or stroke. These medications decrease the activity of vitamin D.
- Bile acid sequestrants (Cholestyramine, Colestipol) are a class of drugs used to lower cholesterol levels. These drugs may reduce the intestinal absorption of fat-soluble vitamins A, D, E, and K.
- Cimetidine (Tagamet and Tagamet HB) prevents the release of hydrochloric acid into the stomach and is used to treat the symptoms associated with stomach and duodenal ulcers and acid reflux. This drug may reduce vitamin D activation by the liver.
- Hormone replacement therapy may increase blood levels of vitamin D.
- The corticosteroids are a family of anti-inflammatory drugs, including hydrocortisone and prednisone, that are commonly used in the treatment of autoimmune and inflammatory diseases, such as asthma, rheumatoid arthritis, and ulcerative colitis. These drugs reduce the activation of vitamin D.
- Heparin, an anticoagulant prescription medication used to prevent blood clots after surgery, may interfere with vitamin D activation.
Vitamin D impacts the following medications:
- Vitamin D may interfere with the effectiveness of calcium channel blockers, a class of drugs used to treat chest pain, irregular heartbeat, and high blood pressure.
- Taking supplemental vitamin D and calcium along with thiazide diuretics can cause blood levels of calcium to increase above normal levels.
How do other nutrients interact with vitamin D?
Vitamin D plays a role in maintaining normal blood levels of calcium. As a result, vitamin D impacts the absorption and storage of calcium. Vitamin D also stimulates the absorption of phosphorus.
Vitamin D is believed to regulate the production of certain calcium-binding proteins that function in the bones and kidneys. Because these binding proteins are dependent on vitamin K, an interrelationship between vitamin D and vitamin K is likely.
It has also been theorized that iron deficiency results in decreased vitamin D absorption.
What health conditions require special emphasis on vitamin D?
Vitamin D may play a role in the prevention and/or treatment of the following health conditions:
- Breast cancer
- Colon cancer
- Ovarian cancer
- Inflammatory bowel disease
- Kidney disease
- Liver disease
- Multiple sclerosis
- Periodontal disease
- Ulcerative colitis
What forms of vitamin D are found in dietary supplements?
The two forms of vitamin D used in dietary supplements are ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3). Ergocalciferol is sometimes considered a vegetarian source of vitamin D since it can be plant-derived. However, yeast is also commonly used as a source of D2, as are other fungi (like ergot). Some individuals would regard these microbially produced forms of D2 as animal-based, while others would not. There's also one "synthetic versus natural" issue involved with supplemental vitamin D. When the plant building block for vitamin D2 (ergosterol)is used to produce vitamin D2 (ergocalciferol), it's usually irradiated in a chemistry lab in order to produce this D2 form.
Cholecalciferol, the D3 form of the vitamin, can be obtained from animal or microbial sources. One common practice for generating the D3 found in supplements involves sheep's wool. Sheep (and many other animals) have sebaceous glands in their skin that secrete a complex variety of substances, including cholesterol (in the form of 7-dehydrocholesterol). The secretions from the sebaceous glands naturally find their way into the animal's fur. A supplement manufacturer wanting to produce vitamin D3 supplements can remove the secretions from the fur (in this case sheep's wool), process and purify the 7-dehydrocholesterol, expose it to UVB (ultra-violet B) light and thereby convert it into cholecalciferol. When it comes to dietary supplements, cholecalciferol is more effective in supporting our vitamin D needs than ergocalciferol. Both forms can produce toxicity if overconsumed.
Vitamin D is often measured in International Units (IU) or micrograms. One microgram of cholecalciferol is equal to 40 IU of vitamin D.
Introduction to Nutrient Rating System Chart
The following chart shows the World's Healthiest Foods that are either excellent, very good or good sources of this nutrient. Next to each food name you will find the following information: the serving size of the food; the number of calories in one serving; DV% (percent daily value) of the nutrient contained in one serving (similar to other information presented in the website, this DV is calculated for 25-50 year old healthy woman); the nutrient density rating; and the food's World's Healthiest Foods Rating. Underneath the chart is a table that summarizes how the ratings were devised. Read detailed information on our Nutrient Rating System.
Introduction to Nutrient Rating System Chart
In order to better help you identify foods that feature a high concentration of nutrients for the calories they contain, we created a Food Rating System. This system allows us to highlight the foods that are especially rich in particular nutrients. The following chart shows the World's Healthiest Foods that are either an excellent, very good or good source of vitamin D. Next to each food name, you'll find the serving size we used to calculate the food's nutrient composition, the calories contained in the serving, the amount of vitamin D contained in one serving size of the food, the percent Daily Value (DV%) that this amount represents, the nutrient density that we calculated for this food and nutrient, and the rating we established in our rating system. For most of our nutrient ratings, we adopted the government standards for food labeling that are found in the U.S. Food and Drug Administration's "Reference Values for Nutrition Labeling."
|World's Healthiest Foods ranked as quality sources of:|
|Salmon, chinook, baked/broiled||4 oz-wt||261.9||411.00||102.8||7.1||excellent|
|Shrimp, steamed/boiled||4 oz-wt||112.3||162.39||40.6||6.5||very good|
|Cow's milk, 2%||1 cup||121.2||97.60||24.4||3.6||very good|
|Cod, baked/broiled||4 oz-wt||119.1||63.50||15.9||2.4||good|
|Egg, whole, boiled||1 each||68.2||22.88||5.7||1.5||good|
What are the current public health recommendations for vitamin D?
In 1997, the National Academy of Sciences established the following Adequate Intake (AI) levels for vitamin D:
- Infants and children: 5 micrograms (200 IU)
- Teenagers: 5 micrograms (200 IU)
- Adults up to 50 years of age: 5 micrograms (200 IU)
- Adults 51-70 years: 10 micrograms (400 IU)
- Adults above 70 years: 15 micrograms (600 IU)
- Pregnant and lactating women: 5 micrograms (200 IU)
A review study (one that summarizes the evidence from a number of other studies) published in the July 2006 issue of the American Journal of Clinical Nutrition found that the currently recommended daily intakes of 200 and 600 IU of vitamin D for younger and older adults, respectively, were insufficient to provide the blood levels of vitamin D needed for bone mineral density, lower-extremity function, dental health, and to lessen risk of falls, fractures, and colorectal cancer.
Adequate blood levels of vitamin D to provide for these health needs begin at 75 nmol/L. Blood levels of vitamin D between 90 and 100 nmol/L are optimal.
Daily intake for all adults of >/=1000 IU vitamin D (cholecalciferol)/d is needed to bring vitamin D concentrations in no less than 50% of the population up to 75 nmol/L. If you are concerned about your vitamin D status, ask your doctor to check your blood levels of 25(OH)D3. The major circulating form of vitamin D in the blood, this form of the vitamin is the true barometer of vitamin D status.
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- Buckley LM, et al. Calcium and vitamin D3 supplementation prevents bone loss in the spine secondary to low-dose corticosteroids in patients with rheumatoid arthritis. Ann Intern Med 1996; 125:961-968.
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- Japanese Conference on the Biochemistry of Lipids. LipidBank. Department of Computational Biology, University of Tokyo, Tokyo, Japan 2007.
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