It isn't safe to eat liver every day, but once or twice a month is not thought to be harmful.
Liver is generally considered a healthy food that's rich in vitamins, minerals, and protein, but it contains high amounts of preformed vitamin A, or retinol. Preformed vitamin A is found in animal products like eggs, milk, and liver. Too much of this type of vitamin A in your diet can cause birth defects in your developing baby, especially during the first months of pregnancy.
The other type of vitamin A is called provitamin A carotenoids, which are found in fruits and vegetables. There's no limit to the amount of carotenoids an expectant mother can safely consume, so you don't have to worry about getting too much vitamin A from fruits and vegetables.
A portion of cow's liver can contain up to three times the maximum daily amount of preformed vitamin A recommended by the United States Department of Agriculture (USDA).
The USDA recommends getting no more than 10,000 IU of preformed vitamin A from supplements, animal sources, and fortified foods – combined – each day. (For women younger than age 19, that number is lower.)
A single serving of cow's liver can contain up to 30,000 IU of retinol. So you could certainly exceed the recommended daily dose if you ate a serving of liver. But you would have to eat that much every day over a period of months to receive a toxic amount of preformed vitamin A.
It's a good idea to avoid daily doses of cod liver oil as well. Years ago it was common for parents to give children cod liver oil because it's rich in vitamins. And now, thanks to the awareness of the benefits of omega-3 fatty acids, found in fish oils, cod liver oil is regaining its popularity (among parents, that is).
Like cow's liver, however, cod liver oil contains large amounts of retinol. A teaspoon of cod liver oil contains 4,500 IU of retinol. If you're interested in taking an omega-3 supplement, ask your doctor for a recommendation.
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