Functional drinks are the new fad, do they really live up to the hype? In this article we examined the science behind some of the claims made by the manufacturers of 3 popular types of drinks: the oxygenated water, vitamin water and coconut water.
Let's start with oxygenated water, in some places it's called hyper or super oxygenated water, as all water is more of less oxygenated. One may ask: can oxygen supplementation improve exercise performance? Yes. It was observed that the BREATHING oxygen DURING exercise could enhance athletic performance (Wagner 1996, Annual Review of Physiology). But the timing of the oxygen supplementation is important, breathing 100% oxygen before or after exercise or during exercise intervals does not aid recovery or enhance performance (Robbins et al. 1992, Medicine and Science in Sports and Exercise). This means that, assuming drinking oxygen is the same as breathing oxygen, you will have be drink the water while exercising. How much oxygen do hyperoxygenated water contain? Well, certainly not 100%
The solubility of oxygen in liquid is very low, it is related to temperature and the pressure at the air-liquid interface (the surface of the water). The oxygen content of bottled water can thus be increased by increasing the pressure inside the bottle. However, once the pressure drops, i.e. the opening of the bottle, the water will start to de-gas quite rapidly, much like carbonated soft drinks. The oxygen content inside the water will consequently fall to normal levels, similar to that of found in tap water. One has to open the bottle to drink the water, therefore even if the oxygen content of the water inside the bottle is significantly higher than in normal water, its oxygen concentration will be greatly reduced by the time it reaches your stomach. One study measured the oxygen concentration in 5 different brands of hyperoxygenated water in SEALED bottles and compared that with the oxygen concentration of normal tap water. It was found that 4 out of the 5 brands did indeed have a higher oxygen concentration as compared to normal tap water (3-9 times higher depends on bands), however one was the same as tap water (Hampson et al. 2003, JAMA). There seemed to be quite a bit of inconsistency in quality between different brands. The highest oxygen concentration in the hyperoxygenated water tested as determined in the Hampson study was only 8%, which is much lower than the 21% oxygen content of the air. This means each litre of hyperoxygenated water contains around 80mL of air, whereas a normal human can inhale roughly 100mL of oxygen with each breath. No wonder Piantadosi proclaimed in the British Journal of Sports Medicine: "A breath of fresh air contains more O2 than a litre of hyperoxygenated water".
One may argue that the extra oxygen in water can be absorbed directly into the body hence have health benefits. That is not true, in fact, there is no conclusive evidence suggesting that oxygen in water could be absorbed by the body. Even if the oxygen did somehow enter the blood stream via the intestines, it would probably enter the veins rather than an artery, which will then be on its way to get re-oxygenated by the lung. It was postulated that for ingested oxygen to have any potential effect on a normal person's systemic oxygen delivery, one would need to provide 250mL of rapidly absorbable oxygen per minute (Piantadosi 2006, British Journal of Sports Medicine). To be able to achieve that, you will have to drink over 3 litres of hyperoxygenated water that contains 9 times higher concentration of oxygen than tap water per minute, and hoping that all oxygen in the water will get absorbed into the blood streams. That's going to be a lot of money spent on water, per minute ;-)
Now, all theories aside, can oxygenated water improve your exercise performance and recovery in a practical setting? The answer is no. There's currently no scientific evidence supporting the notion that consuming hyperoxygenated water can improve exercise performance or aid recovery (McNaughton et al 2007, International Journal of Sports Physiology and Performance; Wing-Gaia et al. 2005, International Journal of Sports Nutrition and Exercise Metabolism; Leibetseder et al. 2006, International Journal of Sports Medicine). It's suggested that the amount of oxygen contained in the water is too low to have any impact on the plasma oxygen levels as hemoglobin (the iron-containing oxygen transport protein in red blood cells) is usually saturated (or close to being saturated) with oxygen during breathing (Jenkins et al. 2002, Medicine and Science in Sports and Exercise). On top of that, the oxygen in the water is likely to be consumed by the cells in the gut before they had any chance of reaching the blood or muscles (Willmert at al. 2002, Journal of Exercise Physiology).
So, what can hyperoxygenated water do? It's good for hydration, just like normal water. Drinking hyperoxygenated water does not have any adverse effects on liver, blood and immune system (Gruber et al. 2005, Clinical Nutrition). Interestingly, studies found that the consumption of hyperoxygenated water could cause a temporary raise in oxygen radicals in the body (Schoenberg et al. 2002, European Journal of Medical Research; Gruber et al. 2005, Clinical Nutrition). This slight raise in oxygen radicals only lasted a short period and only happened to people who don't consume hyperoxygenated water regularly. No potential health implications were mentioned in any of these studies. Hyperoxygenated water is safe for human consumption.
I have to say I liked the idea of vitamin water, it's a neat concept. However, after picking up a few bottles of different flavored vitamin water from the supermarket, and carefully examined their nutritional contents, I started having doubts about whether this is a good idea after all. Here are my reasons:
- Regardless the formulation, vitamin water generally contains a limited number of key vitamins and minerals, and a lot of sugar. Each 500mL bottle contains around 30 grams of sugar, this almost equal to the amount of sugar found in a can of regular coke. If you opt for the sugar-free version, please refer to the aspartame article in the previous edition of this magazine before proceeding further. One may argue that vitamin water is a form of sports drink, and sugar can help with exercise performance (please refer to Are sports drinks beneficial during workouts in the Oct/Nov 2012 edition of the magazine). Of course, having carbs (in the form of sugars) is somewhat important, however, in order for the drink to function as a sports drink, one should also contain a good amount of electrolytes, such as potassium, which is noticeably absent in some of the formulations. Make sure to pick a formulation that contains a good dose of potassium if you wish to use it as a sports drink.
- One other concern I have is the quality and the stability of vitamins in the drinks. There are 2 types of vitamins, water-soluble vitamins, including vitamin B and vitamin C; and fat-soluble vitamins, including vitamin A, D, E and K. Both types of vitamins tend degrade after dissolved in liquid, albeit at different rates. One study investigated the stability of water- and fat-soluble vitamins in vitamin enriched liquid serum and found that after one year of storage at -20 degrees C, up to 30% of the water-soluble vitamins were degraded whereas over 50% of the fat-soluble vitamins were degraded (Ihara et al. 2004, Journal of Clinical Laboratory Analysis). There is no guaranty of the conditions where the vitamin water was stored and transport before they reached the shelves and thus no real assurance of the quality and stability of the vitamins. Indeed, currently available studies investigating the efficacy of the vitamins in vitamin waters only studied the water-soluble vitamins. One study investigated the absorption of vitamin C and B in a commercially available vitamin water and compared to that of the vitamins contained in mixed meals, and found the blood vitamin levels to be identical after consumption (Kalman et al. 2009, International Journal of Food Science and Nutrition). Another study used self-made vitamin C and iron-fortified water and found that it can improve people's nutritional status after 5 months of consumption (Rhoca Dda et al. 2011, Food and Nutrition Bulletin).
Overall, I think the vitamin water currently available on the market is not that dissimilar to the common soft drinks, minus the fizziness. If you want nice tasting water that has a good range of nutrients and antioxidants without all the artificial additives, try fresh juice.
Coconut water, or more scientifically but less appealingly, coconut liquid endosperm has been dubbed by some as one of the worlds most versatile natural products. When I say coconut water here as a drink, I mean the clear, natural, unprocessed, unsweetened liquid taken directly from a fresh coconut, not to be confused with the white coconut milk commonly used in cooking in some of the South East Asian countries. Natural coconut water contains a huge variety of vitamins, amino acids, minerals, fibers, with little fat (less than 0.2%), protein (less than 0.75%) and relative low amount (less than 5%) of sugars (contains a mixture of glucose, sucrose and fructose). The energy content of coconut water is around 79kj per 100g. The sodium content of coconut water varies depending on the growth environment and the age of the coconuts, it can range from 1.75mg/100g of water (results from 1 study) to 105mg/100g of water (results from 3 studies). Many of the nutrients are only found in low levels in coconut water, however, it contains a large amount of potassium, at over 200mg per 100g of water (Yong at al. 2009, Molecules). There is more potassium in 100g of coconut water than that of in a common 600mL (roughly 600g) sports drink. It has been suggested by some that certain contents in coconut water, when used as a pure agent in high doses may have anti-aging, anti-cancer properties in fruit flies or mammalian cell lines. However, I have yet to see any concrete proof to show that the consumption and/or application of coconut water have any such effects in humans.
Coconut water has been found to be able to effectively aid rehydration after exercise induced dehydration and support physical performance in a similar fashion compared to that of a commercially available carbohydrate-electrolyte sports drinks (Kalman et al. 2012, Journal of the International Society of Sports Nutrition). Another recent study evaluated the hypoglycemic and antioxidant effects of coconut water extracted from mature coconuts on diabetic rats. It showed that diabetic animals treated with the coconut water had lower blood glucose levels and reduced oxidative stress (Preetha et al. 2012, Food and Function). Of course, rats are very different to humans and a positive result obtained on rats does not mean it will translate into humans, in fact, in many cases it doesn't. It would be nice to to see similar studies to be conducted on human patients as here is currently no study that demonstrates drinking coconut water has any tangible benefits on human health, other than providing hydration and supply electrolytes.
So all in all, I think coconut water is a healthier alternative to artificially flavored sports drinks, at least it's natural. However, some natural coconut water contains more sodium (salt) per 100mL than sports drinks. We already ingest more than enough salt from our diet and having too much salt can lead to a number of health complications. In addition, the trace amount of vitamins and minerals other than potassium contained in coconut water means that it's not a viable replacement for you daily meals. It's also not very cheap in Australia. However, if coconut water is your thing, make sure the sodium content is low and the drink is not artificially flavored, otherwise, it will be no better than a flavored sports drink.
The purpose of this article is not to "debunk" the myths or glorify benefits of the chosen functional drinks. What I hope to achieve, is to help you looking at products like this in a more rational manner, and to understand that there are no shortcuts for living a healthy life.