We need far more vitamin D than previously thought, according to two teams of researchers from Canada and the U.S.
The Recommended Dietary Allowance (RDA) for vitamin D is ten times lower than what we actually need, say two teams of researchers who have challenged the US's National Academy of Sciences (NAS) and the Institute of Medicine (IOM), both responsible for the RDA.
"The error has broad implications for public health regarding disease prevention and achieving the stated goal of ensuring that the whole population has enough vitamin D to maintain bone health," says Dr. Cederic Garland, an adjunct professor at University of California, San Diego.
Currently the RDA for vitamin D established by the IOM is 600 international units per day until we reach 70 years of age, and 800 IU per day thereafter.
A Canadian research team reviewed each of the 10 studies the IOM used to arrive at their RDA and their calculations revealed that 600 IU of vitamin D per day puts only half of the amount that they had assumed in the blood.
In scientific terms, that means that 97.5 percent of individuals will have serum 25 values of vitamin D above 26.8 nmol/L rather than above 50 nmol/L as the IOM had thought.
To get a serum 25 value of vitamin D of at least 50 nmol/L, you could need up to 8895 IU per day, according to the study.
Dr. Garland's team of US researchers wrote a letter confirming the Canadian team's findings, in which they suggest a slightly more conservative RDA.
"We call for the NAS-IOM and all public health authorities concerned with transmitting accurate nutritional information to the public to designate, as the RDA, a value of approximately 7,000 IU/day from all sources," wrote Dr. Garland and his colleagues.
Dr. Garland added that the number is well below the 10,000 IU currently considered safe by the IOM for teenagers and adults.
Two versions exist: Vitamin D2, known as ergocalciferol, and vitamin D3, also known as cholecalciferol, which is thought to be the more potent and favorable version of the two.
Fatty fish, such as salmon, tuna, sardines and cod liver oil contain hearty amounts of vitamin D3, yet most vitamin D3 is synthesized in the skin upon sun exposure, according to the World Health Organization.
Cereals, cheese and milk could be an important source of both types of vitamin D depending upon where you live yet because they are often fortified with synthetic versions and the amounts may vary.
Vitamin D is important for skin, bone and heart health and deficiencies can result in rickets and abnormal skin pigmentation, yet side effects of excess intake are rare and minimal, according to WebMD.
Both the study and the letter were published in the journal Nutrients.
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If you're going to choose a fish dish, go with salmon. An oily fish high in vitamin D, salmon also has omega 3 fats, protein, vitamin B12 and selenium. "If you eat the soft bones in half a can of salmon (105 grams) you will be consuming almost as much calcium as in a glass of milk," says registered dietitian dietitian Shauna Lindzon.
Another oily fish high in vitamin D and omega 3 fats, mackerel is also rich in vitamins A, B6, B12, C, E and K. Lindzon adds pregnant women, however, should limit mackerel consumption because of its high mercury content.
Sardines are loaded with vitamin B12, selenium, omega 3 fats, protein and vitamin D. "Sardines are very perishable, so eat them when they are fresh," Lindzon says. And since they are smaller fish, they contain lower levels of mercury. Watch out for canned sardines, which may be filled with extra sodium.
Beef liver is a high protein, high cholesterol food choice, Lindzon says. It's high in vitamin B6, B12, and also contains a large amount of dietary iron.
Milk is often called "nature's perfect food", because it's a rich source of many different vitamins and minerals, including calcium, vitamin D and B.
The nutrients in egg yolks differ greatly from egg whites. Egg yolks are high in cholesterol, fat and fat-soluble vitamins including vitamins A, D, E and K.
There are a variety of non-cow milks on the market that are also fortified with vitamin D — perfect for those of you who are vegan or have a lactose intolerance. "Certain brands of soy, rice, almond, and hemp milks have similar vitamins to cow's milk because of the fortification process," Lindzon says.
Mushrooms (all of their edible varieties) have many cancer fighting properties and are a great source of vitamin D.
"When reading labels of breakfast cereals, it is important to choose ones with a high fibre content (more than 4 to 5 grams) and low sugar content (less than 8 grams)," Lindzon says. Adding milk or a milk substitute to a breakfast cereal boosts the calcium, vitamin A, D, and protein content.
There are some orange juices on the market that have calcium and vitamin D added to them. "This fortified orange juice provides people with an option to increase their vitamin intake if they don't consume milk," Lindzon says. However, it is important to note that orange juice lacks the fibre that is in the original orange, and some boxed varieties may have an excessive amount of sugar.
"It is important to check the nutrition labels of yogurts to see if they have vitamin D added," Lindzon says. When choosing yogurts, choose ones that are low in added sugar and high in vitamins.
Cheese is derived from milk, and therefore has the same beneficial vitamins and minerals, including calcium and vitamin D.