Heat, light, exposure to air, cooking in water and alkalinity are all factors that can destroy vitamins.
Vitamins are organic and can be broken down by heat, air, or acid.
Processes that expose foods to high levels of heat, light or oxygen cause the greatest nutrient loss.
Oxidation in water causes water-soluble vitamins and probiotics to degrade with time. Just as nails rust in damp air and apples turn brown when cut open, water soluble vitamins and probiotics degrade when exposed to water and oxygen.
Both the EPA and the FDA recommend mixing the vitamins with another substance such as coffee grounds or kitty litter. This makes the vitamins less recognizable and less desirable, which cuts down on the risk that a child or animal will get into the trash and consume a dangerous amount of the vitamins.
Cooking doesn't destroy it. Vitamin B-12 doesn't break down—even at the boiling point of water—for several hours. A diet low in animal proteins, milk, or dairy foods may increase the need for vitamin B-12.
Vitamin C, also known as ascorbic acid, is a water-soluble vitamin found in fruits and vegetables, including oranges, strawberries, broccoli, tomatoes and green peppers. Vitamin C is easily destroyed by excessive heat and water, as well as exposure to air. Vitamin D, A and K are not destroyed on heating.
While minerals are very stable – vitamins can be degraded in food products. Vitamin degradation is complex and is determined by the matrix of the food/drink. Factors including light, heat, pH and oxygen as well as processing, such as cooking and boiling, can all lead to vitamin degradation.
Vitamin C is a water-soluble and temperature-sensitive vitamin, so is easily degraded during cooking, and elevated temperatures and long cooking times have been found to cause particularly severe losses of vitamin C [12].
Boiling fruits may result in the loss of many vital vitamins. As much as one-half to one-third of vitamins A and C, thiamine and riboflavin are lost in cooking. Soaking fruits can rob them of their nutrients because many of the minerals and vitamins found in vegetables dissolve in water.
Cooking can reduce the nutritional content of veg. It can be a particular problem with vitamin C and the B vitamins and minerals like potassium, because they are water-soluble and so leach out into cooking water.
B-complex vitamins and vitamin C are water-soluble vitamins that are not stored in the body and must be consumed each day. These vitamins can be easily destroyed or washed out during food storage and preparation.
Lack of dietary fat
The absence of dietary fat is likely to reduce the absorption of fat-soluble vitamins. Vitamins are either fat or water soluble. Vitamin D is fat soluble and is stored in fatty tissue; it is usually released as the tissue is broken down by the body.
For example, too much stomach acid may destroy some supplements before they can be absorbed, yet too little acid will not allow for good absorption of certain vitamins, like vitamin B12. Making sure your digestion is well-balanced is essential for good vitamin and supplement absorption.
Celiac disease, inflammatory bowel disease such as Crohn's disease, and many other digestive problems can reduce absorption of nutrients and also lead to deficiencies. And other factors, such as chronic dieting, excessive coffee or alcohol intake, and stress, can deplete vitamins and minerals, fast.
Vitamin B12 is reported to be susceptible to degradation in the presence of ascorbic acid (Frost et al., 1952). The differences in product formulations and processing and/or storage conditions can show varying effects on the stability of vitamin B12 at similar pH.
Even though the B-group vitamins are found in many foods, they are water soluble and are generally quite delicate. They are easily destroyed, particularly by alcohol and cooking.
Vitamin C is easily oxidized acid and destroyed by oxygen, alkali and high temperature.
Vitamin D, A and K are not destroyed on heating.
Any beverage or food containing caffeine such as coffee, tea, chocolate and some sodas can inhibit the absorption of vitamins and minerals and increase their excretion from the body.
[1] People who regularly take medications that suppress stomach acid for conditions like gastroesophageal reflux disease (GERD) or peptic ulcer disease—such as proton-pump inhibitors, H2 blockers, or other antacids—may have difficulty absorbing vitamin B12 from food.
Try to avoid taking your vitamins with coffee or tea
The tannins and caffeine can interfere with the absorption of many vitamins and minerals, especially iron. Caffeine also increases urination, which can decrease the concentration of water-soluble vitamins (B-complex and C).