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Q&A on Cod Liver Oil, Vitamin A, and Vitamin D
Posted by Dr. Ben Kim on Mar 16, 2010
In late 2008, the Vitamin D Council issued a warning on ingesting cod liver oil due to concerns about high levels of vitamin A in many brands of cod liver oil.
What follows are my answers to the most common queries that I received on the Vitamin D Council's paper.
Do you still recommend taking cod liver oil?
Yes, but I can only recommend taking cod liver oil made by Carlson Labs, as this is the brand that I've been taking for several years now. It's also the brand that I have researched most thoroughly.
I'm guessing that there are other quality brands out there - I just haven't spent much time researching and trying other brands because I've been happy with Carlson's product.
What are your thoughts on the Council's position that cod liver oil contains too much vitamin A?
My understanding is that different brands of cod liver oil vary greatly in total vitamin A content.
Carlson cod liver oil contains approximately 800 IU of vitamin A per teaspoon.
Physicians and scientists aren't in agreement on what a safe upper level of vitamin A is for the average adult. Some feel that up to 10,000 IU per day is safe. The Institute of Medical Science has marked 3,000 IU per day as being the recommended daily allowance for male adolescents and adults, and 2,333 IU per day for female adolescents and adults.
My feeling is that the safe upper limit of vitamin A is different for each of us and dependent on overall health status and what we regularly eat.
But generally, if a person doesn't regularly eat large quantities of liver or other organ meats that may be high in vitamin A, I feel that 5,000 IU per day is a safe amount for most adolescents and adults, assuming that vitamin D and other micronutrient statuses are in healthy ranges.
With the 5,000 IU mark in mind, the average adolescent or adult should be able to safely take about 6 teaspoons of Carlson cod liver oil per day. But to tread conservatively and take into account each individual's body weight, I typically recommend taking about 1 teaspoon per 50 pounds of body weight per day.
For those who wish to be even more conservative, my feeling is that taking just 1 teaspoon of Carlson cod liver oil per day is perfectly safe, and provides amounts of vitamin A, D, and omega-3 fatty acids that can make positive differences in overall health status.
Isn't the issue that there is too much vitamin A relative to D in cod liver oil?
Dr. John Cannell, head of the Vitamin D Council, suggests that "The key is having the proper ratio of vitamin D to vitamin A in your body."
Dr. Cannell also suggests that the best way to obtain the proper ratio of vitamin D to vitamin A is to eat a variety of colorful vegetables that are rich in carotenoids, which a healthy body can convert to vitamin A, and to obtain vitamin D by taking "1,000 IU of vitamin D3 per every 25 pounds of body weight in the winter and stop all vitamin D in the summer and sunbathe."
As an alternative to sunbathing when the sun is too low in the horizon to do so, Dr. Cannell suggests using a tanning bed.
Bottom line: The general consensus among members of the Vitamin D Council is that there is too much vitamin A in cod liver oil, enough to increase deleterious effects on vitamin D function and overall health.
The reality - one that all physicians and scientists can agree upon - is that our vitamin A and D levels are constantly in flux, with precise levels determined by what we're eating and how much sunlight we're being exposed to, and this has been true for all humans throughout the history of our world.
In highlighting the importance of maintaining a proper ratio of vitamin D to vitamin A to promote optimal health, my feeling is that Dr. Cannell is encouraging people to rely on natural sources rather than risk disruptions to our health by taking high doses of vitamin A.
The fact that no specific ratio was stated as being optimal supports the idea that the Vitamin D Council's suggestions are meant to encourage avoidance of cod liver oil that contains high levels of vitamin A.
This is why I feel Carlson's cod liver oil is a good choice among the many brands out there - the ratio between vitamin A and vitamin D in Carlson's brand is about 2 to 1. Apparently, there are some brands of cod liver oil that are at 5 to 1 and even 10 to 1.
Why is the ratio between vitamin A and vitamin D different among different brands?
My understanding is that some companies add extra vitamin A or D during the manufacturing process.
Carlson doesn't add any extra vitamin A; the amount of vitamin A in the final product is all naturally occurring.
Carlson does blend in extra vitamin D (from cod liver oil) when necessary to ensure that the final product contains approximately 400 IU of vitamin D per teaspoon.
What is the recommended dose for children?
Ultra-conservative doses are as follows:
For children 2-4 years of age: half a teaspoon of Carlson cod liver oil per day, providing approximately 400 IU of vitamin A.
For children 4 years or older: 1 teaspoon of Carlson cod liver oil per day, providing approximately 800 IU of vitamin A.
For children younger than 2 years of age: I feel that breast milk from a healthy mother is the best source of all nutrients for at least the first 6 months. After the 12-month mark, my feeling is that half a teaspoon of Carlson cod liver oil is a good amount, but it's best to consult with one's personal physician on this.
Why take cod liver oil anyway?
You don't have to take cod liver oil to experience your best health. I use and recommend taking cod liver oil by Carlson because it's an excellent source of omega-3 fatty acids, vitamin A, and vitamin D - if you'd like to know the health benefits of making sure that you are getting enough of these nutrients, please do a quick search for them using the search bar at the top of this page.
When you can get sunlight exposure on bare skin during warmer months, I think it's better to use fish oil, which provides omega-3 fatty acids, but doesn't contain vitamin A or vitamin D.
When sunlight in warm weather isn't available, my feeling is that one needs more vitamin D than what Carlson cod liver oil provides in the doses that I recommend. So on top of taking Carlson cod liver oil whenever one can't make vitamin D from sunlight exposure, it's important to consider getting vitamin D from other sources as well, a good one being a high quality D3 supplement.
How much vitamin D is needed every day for optimal health?
No one knows for sure, and the answer varies for each individual based on health status, diet, and sunlight exposure, but to be conservative, my feeling is that it's best to get at least 1,000 IU per day from all sources (sunlight, diet, supplements).
Recent evidence indicates that even up to about 10,000 IU of vitamin D per day isn't toxic, but my feeling is that it's always best to be conservative, especially when dealing with fat-soluble nutrients like vitamins A, D, E, and K.
A conservative upper limit for vitamin D is about 2,000 IU per day, in my opinion.
Dr. Cannell recommends that people avoid taking vitamin A (not carotenoids) "unless you have a bowel disease that impairs absorption of vegetables and transportation of carotenoids" - what do you think about this?
I've seen enough strict vegans who have relied solely on carotenoids for vitamin A and who have displayed signs of vitamin A deficiency for me to believe that this is the best stance on vitamin A supplementation.
My understanding is that poor absorption of carotenoids is more prevalent than most physicians imagine - more information on this topic can be accessed from the following study:
I think it's certainly possible to meet all of one's vitamin A requirements from carotenoids found in plant foods - it's just not a given for everyone, and all physicians should know this.
Since the main nutrient in question by the Vitamin D Council's report is vitamin A, for reference, here is a table that shows the recommended daily allowance for vitamin A for different age groups and genders, as created by the Institute of Medical Science in 2001:
| Recommended Dietary Allowance
(RDA) for Vitamin A as Preformed Vitamin A (Retinol Activity Equivalents)
|Life Stage||Age||Males: mcg/day (IU/day)||Females: mcg/day (IU/day)|
|Infants (Adequate Intake)||0-6 months||400 (1,333 IU)||400 (1,333 IU)|
|Infants (Adequate Intake)||7-12 months||500 (1,667 IU)||500 (1,667 IU)|
|Children||1-3 years||300 (1,000 IU)||300 (1,000 IU)|
|Children||4-8 years||400 (1,333 IU)||400 (1,333 IU)|
|Children||9-13 years||600 (2,000 IU)||600 (2,000 IU)|
|Adolescents||14-18 years||900 (3,000 IU)||700 (2,333 IU)|
|Adults||19 years and older||900 (3,000 IU)||700 (2,333 IU)|
|Pregnancy||18 years and younger||-||750 (2,500 IU)|
|Pregnancy||19 years and older||-||770 (2,567 IU)|
|Breast-feeding||18 years and younger||-||1,200 (4,000 IU)|
|Breast-feeding||19 years and older||-||1,300 (4,333 IU)|
For a look at the two Carlson products that I use and recommend, please feel free to view the following links:
For information on how to make sure that you're getting enough vitamin D, please view:
If you have any thoughts on this topic, please feel free to share via the comment feature in the article tools box below. Thank you.
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