Fat soluble vitamins are vitamins that dissolve in fats and oils. They are absorbed into your blood better when they are eaten with a fat source and can be stored in the liver and fatty tissues. Unlike water soluble vitamins, fat soluble vitamins are not lost when foods that contain them are cooked.
There are 4 fat soluble vitamins – vitamin A, D, E and K.
Vitamin A is made up of a group of fat-soluble compounds called retinoids, with the most common form being retinol.
Vitamin A has a variety of vital functions in the body including:
- Immunity – important for immune function and deficiency can lead to increased susceptibility to infections
- Vision – helps maintain the light sensitive cells in your eye and is also involved in the formation of tear fluid.
- Growth – essential for cell growth and hair growth and deficiency can lead to hair loss.
- Reproduction – essential for fertility and fetal development.
- Mucous membranes - Our skin, eyes, and mucous membranes of the mouth, nose, throat and lungs need vitamin A to remain moist.
Vitamin A is only found in animal products such as fish liver oil, beef liver, butter and egg yolks. However, vitamin A can also be derived from beta-carotene in foods like carrots, kale and spinach, although it isn’t always converted to retinol (the active form of vitamin A) efficiently.
The RDI is 700 mcg for women and 900mcg for men. The upper limit of vitamin A is 3000mcg for both women and men.
Deficiency can occur in those who eat a plant based diet. As a kid you may have been told to eat your carrots so that you can see in the dark better? Well this is partly true, if you are vitamin A deficient you may have night blindness. More extreme deficiency can lead to dry eyes, blindness, hair loss, skin irregularities and decreased immunity.
Vitamin A toxicity can occur if you consume more than the upper limit of vitamin A supplements or if you eat large amounts of fish liver oil or other liver, however it doesn’t occur if you eat large amounts of beta-carotene from foods such as carrots..
Unlike other vitamins, vitamin D functions like a hormone and every cell in your body has a receptor for it.
It's found in certain foods such as fatty fish (salmon, tuna, sardines), eggs & liver, but it is hard to get enough just from your diet. Our bodies can also produce vitamin D from cholesterol when skin is exposed to sunlight. However, because of the risks of sunburn and skin cancer, we need to be careful how much sun we get.
Vitamin D deficiency is fairly common and around 5% of adults in New Zealand are deficient. A further 27% are below the recommended blood level of vitamin D. This can be due to having dark skin, being elderly, being overweight or obese, not eating much fish or dairy, always using sunscreen when going outside, skin not being regularly exposed to sunlight, living in the South Island, if you have liver or kidney disease, or are on certain medications that affect vitamin D levels.
Vitamin D deficiency can:
- Increase risk of developing colds/infections, particularly respiratory infections
- Cause slow wound healing & increased inflammation
- Cause fatigue/tiredness
- Cause bone/back pain & can cause rickets in children - vitamin D assists with the absorption of calcium
- Can effect mood & increase symptoms of depression
Different people need different amounts of sun exposure to make enough vitamin D. How much sun you should get depends on your skin colour, your age, weight and mobility, your risk of skin cancer, how much vit D you get from your food, if you are taking medications (eg photosensitising meds), the season & certain medical conditions.
You can increase the amount of vitamin D you are getting by eating foods rich in vitamin D and making sure you get outside. This is particularly important now that we are well into winter. Getting outside for some exercise in the sun in the early morning or late afternoon between September & April is recommended by the Ministry of Health if it is safe for you to do so. During May-August this can be done in the middle of the day. Some medical professionals may also prescribe taking vitamin D supplements, especially in the winter for those at risk of having low vitamin D.
Vitamin E is a powerful antioxidant which prevents oxidative stress and protects fatty acids, red blood cells, vitamin A and vitamin K from free radicals. Other nutrients such as vitamin C, vitamin B3 and selenium help enhance the antioxidant properties of vitamin E. It also can increase blood flow by dilating blood vessels which can potentially reduce blood pressure and “bad” LDL cholesterol and decrease the risk of heart disease.
Vitamin E is found in the highest amounts in some vegetable oils, seeds and nuts. Wheat germ oil is particularly high in vitamin E, as well as sunflower oil, sunflower seeds, almonds and hazelnuts.
The RDA of vitamin E for adolescents and adults under 50 years of age is 15mg. For those over 50 the RDA is 12mg
Vitamin E deficiency is very rare for people who are otherwise healthy individuals, as many vegetable oils common on the modern day diet contain vitamin E. Illnesses such as cysctic fibrosis and liver disease which impact the absorption of vitamin E from food, may cause vitamin E deficiency.
If you are getting vitamin E from dietary sources only, it is difficult to overdoes on vitamin E, however if you are taking high doses of vitamin E supplements it can lead to excessive bleeding and increase oxidative stress.
Vitamin K is made up of fat soluble compounds and can be naturally produced by the bacteria in the intestines. It has important roles in blood-clotting, bone health and helping to prevent the calcification of blood vessels which may help reduce the risk of developing heart disease.
Vitamin K1 can be found in green leafy vegetables and vitamin K2 can be found in animal products and fermented soy. Parsley is particularly high in vitamin K1, followed by kale, spinach, Brussels sprouts and lettuce. K2 on the other hand is found in small quantities in some high-fat animal sources such as liver, butter and egg yolks.
Adequate Intake (AI)
The adequate intake for women is 90 mcg and for men 120mcg.
Vitamin K isn’t stored in the body in as high amounts as the other fat-soluble vitamins so you need to get enough in your diet regularly or you could show signs of deficiency in less than one week. Vitamin K deficiency is pretty rare, but there are some things that could prevent you from getting enough vitamin K in your diet. The first is if you do not efficiently absorb fat, such as those with inflammatory bowel disease, celiac disease or cystic fibrosis. Using broad spectrum antibiotics and having very high doses of vitamin A can also effect vitamin K absorption. If you do have vitamin K deficiency your blood won’t clot properly and it may lead to decreased bone density.
Natural forms of vitamin K have no known symptoms of toxicity, but more study is needed to determine a tolerable upper intake.
This week we will have our delicious Roast Brassica Salad in the cabinet which is full of Brussels sprouts, kale and other leafy greens so has a great serving of vitamin K!
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