An overview of vitamins: Water soluble vs Fat soluble. Why do we care about solubility?


Vitamins are categorized into water soluble vitamins and fat soluble vitamins.

Why do we care about the solubility of a vitamin? An understanding of vitamin solubility helps us avoid toxicity from overdose and deficiency from not having enough of a particular vitamin.

1/ Water soluble vitamins:

First of all, water soluble vitamins rarely cause toxicity because the body does not store it like it does to fat soluble vitamins. The excessive amount of water soluble vitamins is usually taken to the kidneys where it’s filtered and removed from the body through urination. So that’s a good thing.

Second, water soluble vitamins show deficiency more quickly than fat soluble vitamins (due to limited storage in the body), which is not necessary a bad thing. However, that means these vitamins demand a steady supply or it will run short quick. When I say quick, it’s pretty much depending on individuals, but usually 6 months to 1 year should be long enough to show signs and symptoms.

Lastly, the water soluble vitamins are known to be unstable substances. For example, vitamin C is very sensitive to heat, but vitamin B2 is sensitive to light only. which makes it a little complicated to meet 100% daily value without care put into meal planning.

There are total 9 water soluble vitamins: vitamin C and  8 B vitamins.

There are total 8 members in the B vitamin group, which are:

  • vitamin B1 (Scientific name: Thiamine)
  • Vitamin B2 (Riboflavin)
  • Vitamin B3 (Niacin)
  • Vitamin B5 (Pantothenic Acid)
  • Vitamin B6 (Pyridoxine)
  • Vitamin B7 ( Biotin also known as vitamin H)
  • Vitamin B9 (Folic Acid, Folate, or vitamin M)
  • Vitamin B 12 (Cobalamin)

The B vitamin family can be further grouped into the energy vitamins and hematopoietic vitamins. The B-complex vitamins, including vitamin B1, B2, B3, B5, and B7 are the ones actively participating in metabolism of carbohydrate, fat, protein, and other metabolism process in the body including blood cell formation, hair growth, skin growth, and nail growth.

The other 3 B vitamins, including vitamin B6, vitamin B9, and vitamin B12, can be called hematopoietic because they are the B vitamins participating in blood cell formation. Because these 3 vitamins have imperative roles in blood cell formation, the deficiency of one these 3 may be enough to cause signs and symptoms of anemia. Anemia is generally understood as low blood red cells due to the lack of dietary iron; however, the  deficiency of either vitamin B6, B9, or B12 may “mask” the nature of anemia. Indeed, if patients are treated anemia with iron supplement while the root of the problem is the deficiency of some hematopoietic vitamins, then the issue will not be addressed.

2/ Fat Soluble vitamins:

Fat soluble vitamins are vitamin A, vitamin D, vitamin E, and vitamin K

Unlike water soluble vitamin, fat soluble vitamins tend to be more stable. At least for most of their forms. Vitamin E is very stable through cooking. The level tends to go down by 20-30% through long term storage (6 months-1 year). Vitamin D level may go down by 50% if you bake or fry something for more than 30 minutes. Vitamin K is possibly the toughest of all when it comes to nutrient retention through storage and heating. However, vitamin K in COOKING OIL is very sensitive to SUNLIGHT. Thus, it’s best to store cooking oil in the fridge or at least in an opaque container if left out on the counter. Well, vitamin A…is a different animal on its own.  Vitamin A, has 2 forms. One is retinoids and the other carotenoids. Retinoids come from animal sources (think egg yolk), which the body is ALWAYS able to convert to useable form for absorption. On the other hand, the other form carotenoids from the plant sources can be converted in our body into retinoids only under CIRCUMSTANCES, before it is absorbed and stored. Out of the two, the carotenoids seems to require the cooking process or breaking down (crushing) for better absorption rather than raw form (which is opposite to most water soluble vitamins that are best when consumed as raw food)

Besides, fat soluble vitamins also require the presence of lipids in form of oil or fat for absorption. If you eat a whole stick of carrot without lipids, you do not get any vitamin A from it. Therefore, it’s best to add a little oil or butter (5 mL per meal) should be sufficient for fat soluble absorption. Some people avoid cooking (raw food people) can still get benefits of these fat soluble vitamins by eating food along with a handful of nuts (a weight of 12 almonds), 50 mL whole milk (please not skim milk), some nut butter (5 grams), or 1/3 of avocado.

Of all the 4 fat soluble vitamins, vitamin D is the only one that can be made by the body using the sun light. When the sun ray hits the skin, the ultraviolet B helps make vitamin D3 (there are also vitamin D1 and D2, but I’ll talk about this more in vitamin D blog). When you use the sunscreen that has UVB protection, you prevent vitamin D3 formation. The ability of the body to make vitamin D3 depends largely on your skin color. The fairer the skin, the faster it takes to produce. If you have fair skin, you need probably 15 minutes or so. If you have the skin of folks from Southeast Asia or East Asia, you’ll need anywhere before 30 minutes to 1 hour depending on your skin color. If you are Nigerian descendent, it may take a couple of hours to produce enough vitamin D with sun exposure. I’m usually not a believer in supplement rather than when I need fast healing power after surgery; however, when I read studies about bone metabolism and osteoporosis, most studies found positive correlation between vitamin D supplement (in the form of vitamin D3 only) and lower osteoporosis risk. So…pop up some vitamin D3!

Rule of thumb: just stick your arms out until it slightly turns pink, then you’re done making vitamin D.


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