Iodine deficiency is one of the most common nutrient deficiencies in the world. In some cases, one serving of a food can meet more than 100% of your daily needs for one or more nutrients. It is essential to choose foods that contain the most nutrients in order to maintain optimal health. Kale is one of the most nutrient-rich foods on the planet and particularly rich in vitamin K1 (vitamins) and C.
A single serving of fresh kale provides a good RDI ratio for these two vitamins. Kombu is another food that has a very high iodine content, with a gram of dried kombu containing 2343 mcg, which far exceeds the RDI. However, it should not be consumed daily as it can cause adverse effects. Vitamin B12 is an essential nutrient for many bodily functions, including cell health, brain and nervous system functioning. The liver contains very high amounts of vitamin B12, vitamin A and copper, but should not be consumed more than once or twice a week.
Selenium is also important for thyroid and immune system function, as well as for antioxidant activity. Clams and oysters are both excellent sources of vitamin B12, which is especially important for older adults. Shellfish are also rich in many other nutrients. Sardines are an excellent source of EPA and DHA, two essential omega-3 fatty acids linked to better heart health.
Vitamin D deficiency is one of the most common nutrient deficiencies in the world, but cod liver oil also contains 270% of the RDI for vitamin A. Vitamin A can be harmful in excessive amounts, so adults are advised not to take more than 2 tablespoons (28 ml) of cod liver oil per day. When it comes to nutrient-dense foods, there are many options available. Kale, kombu, liver, clams, oysters, sardines, cod liver oil, spinach, chia seeds, eggs and yogurt are all incredibly nutrient-rich foods. There are eight B vitamins that play vital roles in the body; salmon, tuna, beef liver, eggs, milk, yogurt, fortified cereals, legumes, nuts and seeds are all excellent sources of one or more B vitamins.
For a quick and nutritious breakfast option there are many healthy options available; oatmeal, eggs, yogurt, smoothies, avocado toast, nut butter toast, quinoa bowls, chia pudding bowls and fruit salad are all great choices. Some nutrient-rich foods can be expensive; however there are many healthy and affordable options available. Beans and legumes (black beans, chickpeas), grains (quinoa), fruits (apples), vegetables (broccoli), nuts (almonds), seeds (chia seeds), dairy products (yogurt), eggs and fish (salmon) are all healthy and budget-friendly options. The various forms of vitamin A are solubilized in micelles in the intestinal lumen and are absorbed by the cells of the duodenal mucosa. Retinyl esters and provitamin A carotenoids are converted to retinol after absorption in the lumen (for retinyl esters) or absorption (for provitamin A carotenoids). Retinol is then oxidized to retinal and retinoic acid - the two main active metabolites of vitamin A in the body - which is mostly stored in the liver as retinyl esters. Retinol and carotenoid levels are generally measured in plasma or serum because blood samples are easy to collect; however these levels are not always reliable indicators of vitamin A status because they do not decrease until vitamin A levels in the liver and other storage sites are nearly exhausted and because acute and chronic infections can reduce serum and plasma concentrations of retinol. Most vitamin A is stored in the liver so measuring vitamin A levels in the liver is the best way to assess vitamin A suitability.
In clinical studies specialized research laboratories can measure the liver's vitamin A stores indirectly using isotopic dilution or dose-response methods. The recommended daily doses of vitamin A are indicated as retinol activity equivalents (RAE) to account for the different bioactivities of retinol and provitamin A carotenoids - all of which the body converts to retinol - see table 2 for details. One mcg of RAE is equivalent to 1 mcg of retinol, 2 mcg of supplemental beta-carotene 12 mcg of dietary beta-carotene or 24 mcg of alpha-carotene or beta-cryptoxanthin in the diet. Table 2 lists a variety of foods and their vitamin A content per serving; animal-based foods mainly contain preformed vitamin A while plant-based foods have provitamin A and foods with a mix of animal and plant ingredients contain preformed vitamin A and provitamin A.NHANES III data conducted between 1988 and 1994 showed that approximately 26% of the vitamin A in RAE consumed by men and 34% consumed by women in the United States comes from provitamin A carotenoids while the rest comes from preformed vitamin A mainly in form of retinyl esters. For an overview of vitamin A and carotenoids see our consumer fact sheet on vitamin A and carotenoids; FoodData Central from Department of Agriculture (USDA) lists nutrient content for many foods providing a complete list ordered by nutrient content or by name.