Vitamin B1 is found in a wide variety of foods at low concentrations. Yeast, yeast extract, and pork are the most highly concentrated sources.
In general, cereal grains are the most important dietary sources of thiamine, by virtue of their wide use. Of these, whole grains contain more vitamin B1 than refined grains, as it is found mostly in the outer layers of the grain and in the germ (which are removed during the refining process). For example, 100 g of whole-wheat flour contains 0.55 mg of thiamine, while 100 g of white flour contains only 0.06 mg of thiamine.
In the US, processed flour must be enriched with thiamine mononitrate (along with niacin, ferrous iron, riboflavin, and folic acid) to replace that lost in processing. In Australia, vitamin B1, folic acid, and iodised salt are added for the same reason.
The few exceptions that are not fortified include organic wholemeal flour (on the assumption that the wholewheat will have kept more of the nutrients).
Some other foods naturally rich in vitamin B1 are oatmeal, flax, and sunflower seeds, brown rice, whole grain rye, asparagus, kale, cauliflower, potatoes, oranges, liver (beef, pork, and chicken)
In studies Vitamin B1 has been shown to have the following properties;
Act as a painkiller in some cases of headache or joint pain.
Improve neurophysiological functions in epilepsy.
Inhibit oxidation of the neurotransmitter dopamine.
Help optic neuritis.
Reduce sensory neuropathy in diabetics.