Daily Dose Of Vitamin D 3

[Senaqua Hildreth]

VitaminD is a nutrient your body needs for building and maintaining healthy bones. That's because your body can only absorb calcium, the primary component of bone, when vitamin D is present. Vitamin D also regulates many other cellular functions in your body. Its anti-inflammatory, antioxidant and neuroprotective properties support immune health, muscle function and brain cell activity.

Vitamin D isn't naturally found in many foods, but you can get it from fortified milk, fortified cereal, and fatty fish such as salmon, mackerel and sardines. Your body also makes vitamin D when direct sunlight converts a chemical in your skin into an active form of the vitamin (calciferol).

The amount of vitamin D your skin makes depends on many factors, including the time of day, season, latitude and your skin pigmentation. Depending on where you live and your lifestyle, vitamin D production might decrease or be completely absent during the winter months. Sunscreen, while important to prevent skin cancer, also can decrease vitamin D production.

Many older adults don't get regular exposure to sunlight and have trouble absorbing vitamin D. If your doctor suspects you're not getting enough vitamin D, a simple blood test can check the levels of this vitamin in your blood.

Taking a multivitamin with vitamin D may help improve bone health. The recommended daily amount of vitamin D is 400 international units (IU) for children up to age 12 months, 600 IU for people ages 1 to 70 years, and 800 IU for people over 70 years.

Without vitamin D your bones can become soft, thin and brittle. Insufficient vitamin D is also connected to osteoporosis. If you don't get enough vitamin D through sunlight or dietary sources, you might need vitamin D supplements.

However, taking too much vitamin D in the form of supplements can be harmful. Children age 9 years and older, adults, and pregnant and breastfeeding women who take more than 4,000 IU a day of vitamin D might experience:

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You stroll down the pharmacy aisles on what seems like a simple mission: pick up some vitamins. But a quick glance at a bottle's label can send you running for a dictionary. Things like "RDA" or "DV" are just a few examples of an alphabet soup that's on many packages. But don't despair. We'll help you demystify supplement guidelines.

Many of the terms you see on labels or supplement websites can help you understand how much of the vitamin or mineral you should take. For example, here are some guidelines set up by the Institute of Medicine:

The RDA (Recommended Dietary Allowance) and the AI (Adequate Intake) are the amounts of a vitamin or mineral you need to keep healthy and stay well-nourished. They're tailored to women, men, and specific age groups.

The UL (Tolerable Upper Intake Level) is the maximum amount of daily vitamins and minerals that you can safely take without risk of an overdose or serious side effects. For certain nutrients, the higher you go above the UL, the greater the chance you'll have problems.

The DV (Daily Value) is the only measurement you'll find on food and supplement labels. That's because space is limited, and there's a need for one single reference number. That number is the amount of a vitamin or nutrient that you should get for top health from a diet of 2,000 calories a day. The DV is sometimes the same as the RDA.

For instance, the average person can take more than 50 times the RDA of vitamin B6 without reaching the upper limit. But some people develop symptoms of nerve pain with these higher levels of B6. So you should always be cautious. Here are some things to keep in mind:

Some supplements are riskier than others. With some vitamins and minerals, the upper limit is pretty close to the RDA. So it's easy to get too much. For example, a man who takes just over three times the RDA of vitamin A would get more than the upper limit. High doses of vitamin A -- and other fat-soluble vitamins like E and K -- can build up in the body and become toxic. Other risky supplements include the minerals iron and selenium.

Supplements are designed to be additions to your diet. Popping pills is not the answer to good health. Experts say you should eat a well-balanced diet and take supplements to fill in any nutritional gaps. Some people take a multivitamin with minerals for nutritional insurance.

The UL is often the limit for all sources of a nutrient. It can include the amount you get from both food and supplements. So when you figure out whether you've reached the UL on a particular nutrient, take into account the food you eat.

You won't find the UL on food nutrition labels or on your vitamin bottle. It's not a number that most people know about. But you'll see it on government websites. And there's a complete list of nutrients with ULs at the end of this article.

Most supplements don't have a UL -- or RDA or DV. The government has only set levels for a fraction of the vitamins and supplements available. For most of the supplements you see on the shelves, experts really don't know the ideal or maximum dose.

Many nutrients, in too high a dose, can be dangerous. To be on the safe side, steer clear of the UL for any nutrient. And if you have a health condition, check with your doctor before you take supplements. They can tell you if they have side effects or interfere with other medicines you use.

The Institute of Medicine has determined upper limits for 24 nutrients. This table is for adults ages 19 or older. It doesn't apply to women who are pregnant or breastfeeding, because they have different nutritional requirements.

Vitamin B12 is a water-soluble vitamin that is naturally present in some foods, added to others, and available as a dietary supplement and a prescription medication. Because vitamin B12 contains the mineral cobalt, compounds with vitamin B12 activity are collectively called cobalamins [1]. Methylcobalamin and 5-deoxyadenosylcobalamin are the metabolically active forms of vitamin B12. However, two others forms, hydroxycobalamin and cyanocobalamin, become biologically active after they are converted to methylcobalamin or 5-deoxyadenosylcobalamin [1-3].

Vitamin B12 is required for the development, myelination, and function of the central nervous system; healthy red blood cell formation; and DNA synthesis [1,4,5]. Vitamin B12 functions as a cofactor for two enzymes, methionine synthase and L-methylmalonyl-CoA mutase [1-3,5]. Methionine synthase catalyzes the conversion of homocysteine to the essential amino acid methionine [1,2]. Methionine is required for the formation of S-adenosylmethionine, a universal methyl donor for almost 100 different substrates, including DNA, RNA, proteins, and lipids [3,5]. L-methylmalonyl-CoA mutase converts L-methylmalonyl-CoA to succinyl-CoA in the metabolism of propionate, a short-chain fatty acid [2].

Intake recommendations for vitamin B12 and other nutrients are provided in the Dietary Reference Intakes (DRIs) developed by the Food and Nutrition Board (FNB) at the National Academies of Sciences, Engineering, and Medicine [1]. DRI is the general term for a set of reference values used for planning and assessing nutrient intakes of healthy people. These values, which vary by age and sex, include the following:

Table 1 lists the current RDAs for vitamin B12 [1]. For adults, the main criterion that the FNB used to establish the RDAs was the amount needed to maintain a healthy hematological status and serum vitamin B12 levels. For infants age 0 to 12 months, the FNB established an AI that is equivalent to the mean intake of vitamin B12 in healthy, breastfed infants.

Plant foods do not naturally contain vitamin B12. However, fortified breakfast cereals and fortified nutritional yeasts are readily available sources of vitamin B12 that have high bioavailability [13,14].

The average vitamin B12 level in the breast milk of women with vitamin B12 intakes above the RDA is 0.44 mcg/L [15]. The U.S. Food and Drug Administration (FDA) specifies that infant formulas sold in the United States must provide at least 0.15 mcg vitamin B12 per 100 kcal [16].

In addition to oral dietary supplements, vitamin B12 is available in sublingual preparations as tablets or lozenges [23]. Evidence suggests no difference in efficacy between oral and sublingual forms [26,27].

Vitamin B12, in the forms of cyanocobalamin and hydroxycobalamin, can be administered parenterally as a prescription medication, usually by intramuscular injection [2]. Parenteral administration is typically used to treat vitamin B12 deficiency caused by pernicious anemia as well as other conditions (e.g., tropical sprue, pancreatic insufficiency) that result in vitamin B12 malabsorption and severe vitamin B12 deficiency [5].

Vitamin B12 is also available as a prescription nasal gel spray. This formulation appears to be effective in raising vitamin B12 blood levels in adults and children [28,29]. A small clinical study with 10 participants (mean age 81 years) found that the bioavailability of a 1,000 mcg cobalamin dose was 2% with intranasal administration, which is similar to the bioavailability of an oral dose [30].

Causes of vitamin B12 deficiency include difficulty absorbing vitamin B12 from food, lack of intrinsic factor (e.g., because of pernicious anemia), surgery in the gastrointestinal tract, prolonged use of certain medications (e.g., metformin or proton pump inhibitors, discussed in more detail below in the section on interactions with medications), and dietary deficiency [5,7]. Because people who have difficulty absorbing vitamin B12 from food absorb free vitamin B12 normally, their vitamin B12 deficiency tends to be less severe than that of individuals with pernicious anemia, who cannot absorb either food-bound or free vitamin B12. Certain congenital conditions, such as hereditary intrinsic factor defects and congenital vitamin B12 malabsorption (Imerslund-Grsbeck disease), can also cause severe vitamin B12 deficiency [5].

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