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    Osteoporosis results from a change in bone mineral density and of bone architecture. These changes come about because the efficiency of the bone remodeling cycle decreases as people get older. It is therefore very important that people have a healthy nutrient intake in order to maintain bone mass. Two of the main nutrients that are beneficial in maintaining the skeleton are calcium and vitamin D. This section is dedicated to vitamin D intake and a discussion of vitamin D rich foods. Information on how vitamin D is created in the body through sunlight activating 7-dehydrocholesterol can be found here.

    Why Vitamin D Supply may be Limited

    It is well known that vitamin D can be created in the body upon exposure to sunlight, so why are people vitamin D deficient?
    Unfortunately, as the body gets older the efficiency of the conversion of 7-dehydrocholesterol by Ultra Violet B light decreases. Additionally people who live in areas where there are seasons, such as in northern USA, Canada, New Zealand and most northern European countries may not receive enough sunlight of an adequate quality to convert vitamin D in the body during the winter months.

    Further to problems associated with latitude it is important to realize that vitamin D is not found in many food products. Therefore, many people may not be receiving adequate supplies of Vitamin D. Some foods such as milk fortified with vitamin D may help to overcome this problem, but many people especially the elderly should also consider taking vitamin D supplements of 400 to 800, or even 1000 ID to help combat osteoporosis.

    Why Vitamin D is Important for Bone Health

    As mentioned in other sections of the site vitamin D is crucial for the biosynthesis of the protein calbindin D9k, this is involved in the facilitated transport of calcium across the cell membrane; this process is especially important when dietary calcium levels are limited. There are many other symptoms of vitamin D deficiency; these include inadequate mineralization of the skeleton, which can result in rickets and osteomalacia.

    A major consequence of vitamin D deficiency is removal of calcium from the skeleton to help balance calcium levels in other parts of the body – as can be imagined this is the last thing that people that have low bone mineral density, and may have osteopenia or osteoporosis, want. Vitamin D deficiency may also lead to weak muscles, and a weakening of bone architecture.

    It is recommended that if you feel that you are not receiving adequate supplies of vitamin D that you incorporate them into your diet either by drinking milk fortified with the vitamin or by taking vitamin D supplements.

    Which Foods are Rich in Vitamin D?

    As mentioned above: most people's main source of vitamin D comes from synthesis in the skin upon exposure to UV light. The newly created vitamin D then travels through the body and is hydrolyzed first in the liver, and then in the kidney.

    Vitamin D is involved in the regulation of calcium in the body, and therefore has major benefits with regards to bone building and retention.

    Usually a 15-minute exposure to sunlight twice a week is enough to give a person an adequate supply of vitamin D. However, in the winter, when skies are cloudy, the weather is cold, and the strength of the sun is less, many people do not receive adequate amounts of vitamin D.

    Many people turn to vitamin D supplements, this is usually because there are not that many vitamin D rich foods. One of the best sources of vitamin D are fish and liver, therefore taking a capsule of cod liver oil daily is an ideal way of getting the nutrient for non-vegetarians.

    As there are not many foods that naturally contain vitamin D it is often the case that foods are fortified with the vitamin, goods that are commonly fortified with vitamin D include milk and cereals.

    Natural vitamin D rich foods include fish and egg yolks. It is also possible to have vitamin D rich mushrooms; these are grown in the presence of UV light thus enabling the mushroom to synthesize the vitamin. Due to vitamin D being largely contained in animal-related products, it is often the case that vegans suffer from vitamin D deficiency. In addition to the mushrooms, other good sources of vitamin D for vegans include fortified soymilk, and yeast. Unfortunately, fortified vitamin D, and the best vitamin D supplement suitable for vegans tends to be in the less efficiently absorbed D2 form, and not the D3 (D3 is dreived from animal products); it is therefore very important that vegans try to get out into the sunlight as much as possible in the winter months at high latitudes. Here is a full Vitamin D food list.

    List of Vitamin D Content in Various Foods

    Food sources of Vitamin D
    Food
    Quantity
    Vitamin D IU
    Natural Foods
    Beef Liver
    100g (4oz)
    53
    Cod
    100g (4oz)
    140
    Cod Liver Oil
    1 Tablespoon
    1350
    Cod Liver Oil
    1 Capsule
    50 to 150 (depending on brand and size)
    Egg Yolk
    1 (medium)
    25
    Grey Soul
    100g (4oz)
    75
    Mackerel
    100g (4oz)
    520
    Salmon, Atlantic (Fresh)
    100g (4oz)
    300
    Salmon, Sockeye (Red Salmon) (Fresh)
    100g (4oz)
    1060
    Salmon, Atlantic (Tinned)
    100g (4oz)
    94
    Salmon, Sockeye (Red Salmon) (Tinned)
    100g (4oz)
    480
    Sardine (tinned)
    4 sardines
    94
    Trout (farm)
    100g (4oz)
    520
    Trout (wild)
    100g (4oz)
    1050
    Tuna, Skipjack (fresh)
    100g (4oz)
    510
    Tuna, Bluefin (fresh)
    100g (4oz)
    920
    Tuna, albacore (tinned)
    100g (4oz)
    55
    Tuna, light (tinned)
    100g (4oz)
    140
    Grown in UV light
    Mushrooms
    100g
    535
    Fortified Foods
    Cheese (Usually Swiss or Edam that are fortified)
    100g (4oz)
    24
    Margarine
    1 desert spoon (12ml)
    48
    Milk
    100ml
    50
    Milk
    1 cup (240ml)
    120
    Orange Juice (varies on product)
    100ml
    40
    Orange Juice (varies on product)
    1 cup (240ml)
    100
    Soy Milk
    100ml
    50
    Soy Milk
    1 cup (240ml)
    120
    Tofu
    100g (4 ounces)
    65
    Yogurt
    150g (6oz)
    80

    Nb. Farmed Salmon has only 25% the vitamin D content of wild salmon. Farmed Trout has about 50% the content of wild.

    The Effect of Cooking Fish on Vitamin D Levels

    Cooking fish can have a derogatory effect upon vitamin D levels. Baking fish is the best way of maintaining vitamin D levels and typically reduces the amount of vitamin D by just 2%. Frying fish on the other hand can reduce vitamin D levels to just 50% of their fresh levels.

    How Much Vitamin D to Take

    Ideally men and women aged from 18 to 70 should have an intake of 15 micrograms (600IU) a day to maintain bone strength; for people over the age of 70 the RDA is 20 micrograms (800IU). The maximum RDA was raised from 2000 IU to 4000 IU by the institute of medicine. The recommended serum levels of vitam D for sustained bone health is given as greater than 20 ng/ml. Many in the medical field feel that this serum amount is too low, as it only takes into account bones; the previous recommendation used by the IOM used to be 32 ng/ml. This is the level that the Linus Pauling Institute recommends; they also suggest that adults living at high lattitudes take 2000 IU of vitamin D per day.

    Vegans and Vitamin D Revisited

    Due to not eating fish and dairy products, vegetarians, and especially vegans, need to ensure that they get adequate supplies of calcium and vitamin D. As the vitamin is not found naturally in vegetables, it is recommended that vegans who are unable to get an adequate supply of vitamin D via exposure to sunlight, drink soya milk, tofu or cereals that have been fortified, or eat mushrooms that have been grown to be vitamin D rich; or take a supplement.

    References

    Cashman (2007). Diet, Nutrition and Bone Health. Journal of Nutrition. Supplement: 2507S to 2512S
    Cashman (2003). Prebiotics and calcium bioavailability. Curr Issues Intest Microbiol. 4: 21 to 32.
    Department of Health (1998). Nutrition and bone health with reference to and vitamin D. Dietary reference values for food energy and nutrients for the United Kingdom.
    Webb et al (1988). Influence of season and latitude on the synthesis of vitamin D3: exposure to winter sunlight in Boston and Edmonton will not promote vitamin D3 synthesis in human skin. J Clin Endocrinol Metabolism. 67: 373 to 78.