"Vitamin pills are useless within a week of opening," the Daily Mail reported. It said that the high levels of humidity in kitchens and bathrooms make them simply dissolve even if the bottle’s lid is screwed on.
This research studied the breakdown of two common forms of vitamin C under different temperatures and humidities in the laboratory, and found that high humidity seemed to have the greatest effect.
Though the effect seen in this lab study may also occur in supplements used at home, it is not clear if the different forms of vitamin C will degrade at the same rate. Supplements usually contain other nutrients, minerals and ingredients, some of which are preservatives. For example, silica, which absorbs water, is often included.
Further research into the best storage conditions for vitamins is likely. The most useful would be testing the rate of vitamin C degradation in different formulations, and under conditions found in the home. For now, the best way to store vitamins is in their original container in a cool, dry place. Kitchens and bathrooms may not be the best storage places.
The research was carried out by Ashley Hiatt and colleagues from Purdue University, Indiana, US. The research was supported by grants from the US Department of Agriculture and from Lilly Endowment, Inc. – a private philanthropic foundation set up through gifts of stock in Eli Lilly, a pharmaceutical company. The paper was published in the peer-reviewed Journal of Agricultural and Food Chemistry .
The newspapers have generally reflected these findings, without going into the complexities of the laboratory research. However, Metro’s headline that stored vitamins “go off in a week” may be misleading, as the research looked at how vitamin C breaks down, and its positive effects on the body, and not that it becomes harmful or 'goes off'. This research was also in raw vitamin C – sodium ascorbate and ascorbic acid – and not in vitamin supplements. Supplements tend to contain other ingredients, which may alter the rate at which vitamin C breaks down.
This laboratory study aimed to model the degradation (breakdown) of vitamin C and to investigate how variations in humidity and temperature affect this. Vitamin C is one of the most widespread nutrient supplements, but is also highly unstable and quickly degraded by exposure to heat, light and air. As such, vitamin C is commonly monitored when determining shelf life.
The researchers say that a study looking at the degradation of vitamin C though exposure to heat and humidity would be valuable. In particular, it would help to understand the process by which vitamin C in storage absorbs moisture from the atmosphere to form a solution, known as deliquescence (when a substance melts or becomes liquid).
The researchers studied the two most common forms of vitamin C, sodium ascorbate and ascorbic acid, which have different deliquescence points. Complex laboratory methods were used to analyse both forms. This involved storing the vitamin C in a chamber above different saturated salt solutions to give different humidity exposures and exposing it to temperatures ranging from 4C to 40C.
After the different exposures, the researchers measured the breakdown of vitamin C using colourimetry, a form of photometric analysis that indicates the concentration of vitamin C present. The amount of moisture that had been absorbed was measured using a different type of analysis (known as gravimetric sorption analysis). The two forms of vitamin C were also analysed over an extended period of eight weeks at different temperature and moisture conditions, and regularly assessed to see at which point they achieved 50% degradation – their half-life.
Both humidity and temperature significantly affected the stability of vitamin C, but humidity had the greatest effect.
The researchers say this indicates that the two forms of vitamin C are affected by different combinations of humidities and temperatures. Moisture absorption appeared to precede extensive breakdown, and was considered to be a good predictor of vitamin C loss.
The researchers conclude that it is important to consider the phases of transformation that vitamin C goes through during storage when considering the shelf life of a nutrient supplement. They say that it is important to ensure it is maintained in the solid state “for enhanced stability”.
This research examined the breakdown of two common forms of vitamin C under controlled temperature and humidity conditions in the laboratory. It found that, of temperature and humidity, high humidity seemed to have the greatest effect on vitamin C breakdown. Generally, ascorbic acid was more stable than sodium ascorbate under the conditions tested in this study.
The breakdown of vitamin C does not mean that it becomes harmful or past its use-by date, but it does raise the question of whether or not the nutrients remain beneficial. This research was in two ‘raw’ forms of vitamin C, sodium ascorbate and ascorbic acid, studied in the laboratory. It is well-established knowledge that vitamin C is an unstable and easily degradable substance.
Often in supplements, vitamin C will be formulated with other nutrients and vitamins, in addition to other ingredients, some of which are preservatives (for example silica, which absorbs water). Though the effect found in this study may be replicated in bathroom cabinets and kitchens, it is not clear if vitamin C will degrade at the same rate when formulated with other ingredients and under home conditions.
Further research into the best storage conditions for vitamins is likely to occur. For now, the best way to store vitamins is in their original container in a cool, dry place. Kitchens and bathrooms often do not meet these requirements so may not be the best storage places.