Intro (00:09:24)

Science on the Menu, a podcast by the European Food Safety Authority.

Ed (00:21:03)

Hello and welcome to another episode of Science on the Menu, a podcast by EFSA, the European Food Safety Authority. My name is Ed Bray, and I work in EFSA's communications unit. And today, I'm joined by Silvia Valtueña from EFSA's human nutrition team. Hi Silvia, how are you doing?

Silvia (00:41:12)

Hi Ed, very well. How are you doing?

Ed (00:43:11)

Yeah, I'm very well, thank you. And I'm really looking forward to this conversation. Today, we're going to be talking about hydration, a very topical subject right now, given that we're coming into the summer season. And we hear a lot about hydration and the fact that it's important, but maybe some of us don't know actually what it really is. So that's my first question to you. What is hydration, actually?

Silvia (01:09:18)

Well, hydration is the maintenance of an equilibrium between the water and electrolytes we have in the body. We need to have the right concentration, the right amount. So that means an equilibrium between the water that goes in, and the water that goes out.

Ed (01:25:02)

When you're talking about the water that goes out. You're talking about going to the bathroom?

Silvia (01:29:15)

Going to the bathroom, through urine and feces, but also sweating or breathing. We can lose huge amounts of water through those.

Ed (01:39:10)

And you said that it's an equilibrium. So, it's a balance, actually. Hydration is keeping the body in a state where these levels are balanced. Is that right?

Silvia (01:51:09)

Yeah, that's correct.

Ed (01:52:08)

And I imagine then that when we become dehydrated, we're out of balance. Is that right?

Silvia (01:57:06)

We are. Either because we lose water, salts, or both, and we are not able to restore them on time. You know, it depends on the level, the consequences of dehydration, because if we lose 1% of the water, more or less, in one day, that is very easy to restore. So, we don't even feel it because the function is so important that we have a lot of control mechanisms to make sure that we maintain the balance. If water and electrolytes and salts, to say it in an easy way, are not restored on time and we keep losing them, then we start feeling sleepy, dizzy, getting a headache. And if this goes on, it can have really adverse consequences on health.

Ed (02:43:19)

Okay. Can you talk about some of those consequences?

Silvia (02:46:10)

Well, you could die. That could be the worst one. Or you end up in an emergency room to get hydrated, rehydrated. And also, rehydration is very complicated, it is not about water, particularly if you lost also salts. So, you need to do it in the right way because incredibly enough, if you get rehydrated only with water very quickly, you could have water intoxication, which is a very rare consequence that in normal conditions you will need to drink like 25 liters of water per day to exceed the concentration of the kidney, the concentration capacity of the kidney. We never see this. I mean, it's very rare. But water intoxication because of a wrong rehydration, that is more common.

Ed (03:33:21)

And what role does EFSA have then in the field of hydration and water? Is there some work that we've done that is providing scientific advice?

Silvia (03:46:02)

There is, yes. We have an opinion on reference values for water. And that means that it is about the water that should go in from food and beverages, not only beverages. Of course, the values change with age and sex. But to give you an idea, for adults, these are more or less 2.5 liters for men, a little less for women, 2 liters. But of course, you need to set conditions for that because water needs may change dramatically depending on certain conditions, for example, climate and physical activity. So those values are for moderate conditions of both.

Ed (04:27:20)

And you said that's a reference value. So, what does that mean actually? Does that mean that every day I need to be drinking two liters? Or what happens to that reference value after that for consumers to understand how much they need to be drinking?

Silvia (04:45:06)

Well, this is what you need on average daily under the conditions I said before, because, of course, as you know, there are many factors affecting those values. Factors affecting mostly water losses, and that is temperature, so the climate, whether it’s very hot or not, physical activity, whether it is intense or not. But also, what we eat. For example, you know, we all had this experience of eating a very salty meal maybe, and then drinking like crazy because we need that water to get rid of the salt. So, there are many factors, also disease, also in summer when it's very hot and people get the typical gastrointestinal infection, start vomiting, diarrhea. Their water loss increases a lot, and then the two liters or two liters and a half are not enough of course.

Ed (05:38:02)

And so, I understand from that that it's also about the food that you're eating. So, if you're eating a lot of fruit in the summer, you are actually hydrating yourself as well.

Silvia (05:45:12)

Better. Yes, because 90% of fruits and vegetables are water. But when those requirements increase a lot, the easiest way to compensate is through drinking.

Ed (05:57:06)

And then what would be the best way to hydrate yourself? Would it be to take on board water little and often or to drink a large amount in the morning. What would you recommend in that case?

Silvia (06:10:22)

Well, it depends on who you are and what you're doing. Under normal conditions, it doesn’t matter really. I mean, whether you drink with meals, before meals after meals, whether you drink big amounts in one go, or you're sipping the whole day like Americans sipping coffee. But under certain circumstances, for example, if you are a high intensity physical worker or you’re an elite athlete doing a competition, in those circumstances, it does make a difference. There, their condition is to drink little amounts very often and not only water, but also electrolytes and maybe sugars, carbohydrates to get energy. You need to keep going for physical performance because otherwise, you start digestion and a big amount of blood from your body is going to go from the muscles to the stomach and you are going to decrease your physical performance dramatically.

Ed (07:08:07)

Wow, that's really interesting, that's why, or probably why, you see these elite athletes with these specialist drinks that they are constantly sipping from.

Silvia (07:17:07)

Exactly. That's the reason.

Ed (07:19:14)

Yeah, that's really interesting. I'm actually feeling a little bit dehydrated right now. I would say I feel a bit thirsty. What would be going on with me right now, do you think, with my body?

Silvia (07:30:09)

Well, in this case, very little, you may concentrate less, which is not a very good thing for the podcast actually! But not much. You will need to lose a lot more water for that. And this doesn't happen under normal conditions because as I said we have a lot of control mechanisms, the first of them is that you are feeling thirsty and therefore you will be drinking, right? So not much.

Ed (07:56:13)

And if I was now to go, I'm not going to do this, but if I was going to go and have a beer or another type of alcohol, or perhaps go and drink a lot of coffee, what impact would that have on my status of hydration?

Silvia (08:09:18)

Well, the immediate impact would be that you will get rehydrated because you are getting volumes of water. But both caffeine and alcohol foster urine, so the loss of water through urine, through different mechanisms, so the combination would do that even more. In any case, unless you're a heavy caffeine or alcohol, coffee, or alcohol drinker, you don’t need to drink a lot more to compensate for that. But if you are, and you are both, your intake of water may need to increase because you will be losing more.

Ed (08:42:16)

Okay, that's interesting. So maybe best to take some water while you have a coffee, think about drinking some other fluids while you're drinking alcohol, correct?

Silvia (08:52:16)

Yes, but it doesn't make, in that case with moderate consumption, doesn't make a big difference.

Ed (08:57:24)

I've got a general question for you that I think could have an impact on hydration and the kind of advice that maybe a health body gives in the future and that's related to the change in climate. We know temperatures are rising and we see higher summer temperatures, particularly in the north, for example, where maybe they are not used to high temperatures in the summer. Do you think this is going to impact on how we think about hydration in the future? 

Silvia (09:23:21)

I think it will, definitely, because we need to increase the volume of liquids we introduce. The source of those liquids is going to become more and more important, not only for hydration, but for nutrition, actually.

Ed (09:38:17)

And you mentioned some of the vulnerable groups, who need to think about this even more. Can you talk a little bit more about that? Those groups that really need to pay special attention to hydration.

Silvia (09:49:03)

Of course, one will ask who those are, right? 

Ed (09:51:00)

Yeah. 

Silvia (10:53:20)

And from what I said before, we can think immediately about small babies, infants, and also the elderly, for the same reasons actually. In the first case, they have difficulties in expressing that they are thirsty and the mothers understanding that, and they have a lower capacity to concentrate urine and that happens in the elderly as well but in that case, you lose the sense of thirst with aging. So, even if they get dehydrated, they don't feel thirst, so they should be drinking, even if they are not thirsty.

Ed (10:24:19)

Okay, that's interesting. So, they maybe even need to set reminders for themselves to remember.

Silvia (10:29:16)

They do, yes. Actually, in nursing homes, they are quite strict about that because there are several cases of dehydration because of that problem. If you allow me, I want to add one thing about the babies, because, of course, the 1 million question is always breastfeeding versus infant formula. For breastfed infants, they get the water they need through breast milk, they don't need additional. But if we are making infant formula, we need to be very careful about the diluting proportions that are indicated by the manufacturers, because you know, that was happening more often in the past after the war, that women thought the more nutrition they were giving, the better. But that is a real problem for hydration. Infants were getting dehydrated if you give more powder than water than is recommended, so very careful there.

Ed (11:17:20)

Oh, that's interesting. That's a good recommendation then to parents listening.

Silvia (11:20:19)

Yes.

Ed (11:23:01)

And one final personal question to you. How did you get into this field, actually, of work?

Silvia (11:28:10)

Oh, well, that's a good question. You know, I'm a medical doctor by education, but when I finished the medical school, I realised I didn't want to practice medicine, that was not what I was really willing to do. So, I wanted to enter the research field and there, I realised very quickly that the knowledge among medical doctors about nutrition, I'm talking about 30 years ago, was not that high. And that was giving me a possibility of having a very unique profile. And I must say, I really enjoyed it a lot. It was a great, great choice, I think.

Ed (12:04:24)

Well, we're glad, we're very glad to have you at EFSA I think, as well, to have your expertise. Okay. Well, I think that's all we have time for today. So, thanks very much, Silvia, for giving us all these recommendations, a behind the scenes look at actually what hydration is. Hopefully, we understand it better now. To all our listeners, please do subscribe to the podcast and we look forward to seeing you again soon for a new episode of Science on the Menu.

Silvia (12:30:16)

Thank you, Ed.

Ed (12:31:10)

Thanks very much and goodbye.