Water is essential for daily functioning and health, and we can only survive a few days without it. Yet we constantly lose water through sweat, urination and even evaporation when we breathe.

This is why we have evolved a way to regulate and maintain water in our bodies. Like other animals, our survival relies on a strong biological drive that tells us to find and drink water to balance fluid loss.

This is thirst – a sensation of dryness in the mouth signalling we need to have a drink. This basic physiological mechanism is controlled mainly by part of the brain’s “control centre”, called the hypothalamus. The hypothalamus receives signals from various regions of the body and in return, releases hormones that act as a messenger to signal the thirst sensation.

What is dehydration?

Staying hydrated (having enough water in our bodies) is important for several reasons, including:

• regulating body temperature through sweat and respiration
• lubricating joints and eyes
• preventing infections
• digesting and absorbing nutrients
• flushing out waste (via the kidneys)
• preventing constipation
• brain function (including memory and concentration)
• mood and energy levels
• physical performance and recovery from exercise
• skin health.

Dehydration occurs when our body doesn’t have enough water. Even slight drops in fluid levels have noticeable consequences, such as headaches, feeling dizzy, lethargy and struggling to concentrate.

Chronic dehydration can pose more serious health risks, including urinary tract infections, constipation and kidney stones.

What does the evidence say?

Despite thirst being one of the most basic biological drivers for good hydration, science suggests our feelings of thirst and subsequent fluid intake don’t always correlate with hydration levels.

For example, a recent study explored the impact of thirst on fluid intake and hydration status. Participants attended a lab in the morning and then later in the afternoon to provide markers of hydration status (such as urine, blood samples and body weight). The relationship between levels of thirst in the morning and afternoon hydration status was negligible.

Further, thirst may be driven by environmental factors, such as access to water. For example, one study looked at whether ample access to water in a lab influenced how much people drank and how hydrated they were. The link between how thirsty they felt and how hydrated they were was weak, suggesting the availability of water influenced their fluid intake more than thirst.

Exercise can also change our thirst mechanism, though studies are limited at this stage.

Interestingly, research shows women experience thirst more strongly than men, regardless of hydration status. To understand gender differences in thirst, researchers infused men and women with fluids and then measured their thirst and how hydrated they were. They found women generally reported thirst at a lower level of fluid loss. Women have also been found to respond more to feeling thirsty by drinking more water.

Other ways to tell if you need to drink some water

While acknowledging some people will need to drink more or less, for many people, eight cups (or two litres) a day is a good amount of water to aim for.

But beyond thirst, there are many other ways to tell whether you might need to drink more water.

1. urine colour: pale yellow urine typically indicates good hydration, while darker, concentrated urine suggests dehydration

2. frequency of going to the toilet: urinating regularly (around four to six times a day) indicates good hydration. Infrequent urination can signal dehydration

3. skin turgor test: gently pinching the skin (for example, on the back of the hand) and observing how quickly the skin returns to its normal position can help assess hydration. Slow return may indicate dehydration

4. mouth and lips: a dry mouth or cracked lips can be early signs of dehydration

5. headaches and fatigue: frequent headaches, dizziness, or unexplained fatigue can be signs of inadequate hydration

6. sweating: in physically active people, monitoring how much they sweat during activity can help estimate fluid loss and hydration needs. Higher levels of sweat may predispose a person to dehydration if they are unable to replace the fluid lost through water intake

These indicators, used together, provide a more comprehensive picture of hydration without solely depending on the sensation of thirst.

Of course, if you do feel thirsty, it’s still a good idea to drink some water.

Lauren Ball, Professor of Community Health and Wellbeing, The University of Queensland and Kiara Too, PhD candidate, School of Human Movement and Nutrition Sciences, The University of Queensland

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Drug companies are paying Australian doctors millions of dollars a year to fly to overseas conferences and meetings, give talks to other doctors, and to serve on advisory boards, our research shows.

Our team analysed reports from major drug companies, in the first comprehensive analysis of its kind. We found drug companies paid more than A$33 million to doctors in the three years from late 2019 to late 2022 for these consultancies and expenses.

We know this underestimates how much drug companies pay doctors as it leaves out the most common gift – food and drink – which drug companies in Australia do not declare.

Due to COVID restrictions, the timescale we looked at included periods where doctors were likely to be travelling less and attending fewer in-person medical conferences. So we suspect current levels of drug company funding to be even higher, especially for travel.

What we did and what we found

Since 2019, Medicines Australia, the trade association of the brand-name pharmaceutical industry, has published a centralised database of payments made to individual health professionals. This is the first comprehensive analysis of this database.

We downloaded the data and matched doctors’ names with listings with the Australian Health Practitioner Regulation Agency (Ahpra). We then looked at how many doctors per medical specialty received industry payments and how much companies paid to each specialty.

We found more than two-thirds of rheumatologists received industry payments. Rheumatologists often prescribe expensive new biologic drugs that suppress the immune system. These drugs are responsible for a substantial proportion of drug costs on the Pharmaceutical Benefits Scheme (PBS).

The specialists who received the most funding as a group were cancer doctors (oncology/haematology specialists). They received over $6 million in payments.

This is unsurprising given recently approved, expensive new cancer drugs. Some of these drugs are wonderful treatment advances; others offer minimal improvement in survival or quality of life.

A 2023 study found doctors receiving industry payments were more likely to prescribe cancer treatments of low clinical value.

Our analysis found some doctors with many small payments of a few hundred dollars. There were also instances of large individual payments.

Why does all this matter?

Doctors usually believe drug company promotion does not affect them. But research tells a different story. Industry payments can affect both doctors’ own prescribing decisions and those of their colleagues.

A US study of meals provided to doctors – on average costing less than US$20 – found the more meals a doctor received, the more of the promoted drug they prescribed.

Another study found the more meals a doctor received from manufacturers of opioids (a class of strong painkillers), the more opioids they prescribed. Overprescribing played a key role in the opioid crisis in North America.

Overall, a substantial body of research shows industry funding affects prescribing, including for drugs that are not a first choice because of poor effectiveness, safety or cost-effectiveness.

Then there are doctors who act as “key opinion leaders” for companies. These include paid consultants who give talks to other doctors. An ex-industry employee who recruited doctors for such roles said:

Key opinion leaders were salespeople for us, and we would routinely measure the return on our investment, by tracking prescriptions before and after their presentations […] If that speaker didn’t make the impact the company was looking for, then you wouldn’t invite them back.

We know about payments to US doctors

The best available evidence on the effects of pharmaceutical industry funding on prescribing comes from the US government-run program called Open Payments.

Since 2013, all drug and device companies must report all payments over US$10 in value in any single year. Payment reports are linked to the promoted products, which allows researchers to compare doctors’ payments with their prescribing patterns.

Analysis of this data, which involves hundreds of thousands of doctors, has indisputably shown promotional payments affect prescribing.

US research also shows that doctors who had studied at medical schools that banned students receiving payments and gifts from drug companies were less likely to prescribe newer and more expensive drugs with limited evidence of benefit over existing drugs.

In general, Australian medical faculties have weak or no restrictions on medical students seeing pharmaceutical sales representatives, receiving gifts, or attending industry-sponsored events during their clinical training. They also have no restrictions on academic staff holding consultancies with manufacturers whose products they feature in their teaching.

So a first step to prevent undue pharmaceutical industry influence on prescribing decisions is to shelter medical students from this influence by having stronger conflict-of-interest policies, such as those mentioned above.

A second is better guidance for individual doctors from professional organisations and regulators on the types of funding that is and is not acceptable. We believe no doctor actively involved in patient care should accept payments from a drug company for talks, international travel or consultancies.

Third, if Medicines Australia is serious about transparency, it should require companies to list all payments – including those for food and drink – and to link health professionals’ names to their Ahpra registration numbers. This is similar to the reporting standard pharmaceutical companies follow in the US and would allow a more complete and clearer picture of what’s happening in Australia.

Patients trust doctors to choose the best available treatments to meet their health needs, based on scientific evidence of safety and effectiveness. They don’t expect marketing to influence that choice.

Barbara Mintzes, Professor, School of Pharmacy and Charles Perkins Centre, University of Sydney and Malcolm Forbes, Consultant psychiatrist and PhD candidate, Deakin University

This article is republished from The Conversation under a Creative Commons license. Read the original article.