'The link between the flu and mental health I had no idea about.'

My back hurts. My face is… full. I’ve lost my appetite (which never happens. No, like, actually never). 

I have the goddamn flu and no one cares nearly as much as they should.

It’s been widely described as the worst flu season in years, and if you haven’t been struck down yourself in the last few weeks, it’s likely you know someone who has. And while we’re all aware of the flu-ey symptoms that form the backdrop of every winter, this year I’ve noticed something different: mood.

While I’ve been sick, I’ve also felt more miserable than I have in years. I want to cry all the time. I don’t want to leave the house, I’m sleeping all hours of the day, and there’s absolutely nothing I can think of doing that would give me joy.

At first, I was genuinely worried. And scared. My mental health was taking a deep dive and I felt like I wasn’t able to do anything about it.

But after speaking with family and friends, I discovered something interesting – feeling seriously, seriously down when you’re sick with the flu (and even for the period immediately after) is fairly common. And there’s a fascinating reason for it.

I spoke to Dr Brad McKay, an experienced family doctor, about what he witnesses in his patients, and why the flu seems to have such a profound impact on people’s moods.

"I frequently have patients coming to the clinic not only suffering from influenza, but also feeling incredibly depressed," he said. "Fortunately in most cases, once they start to feel physically better, their mood returns to normal after a few more days."

There's actually physiological reason for feeling depressed when you have the flu.

"Influenza viruses are identified by your immune system which stimulates white cells to start producing inflammatory proteins called cytokines," McKay explained. "Cytokines help fight off infection but also make you feel terrible in the process."

"A large release of cytokines into your body gives you a high fever, muscular aches, fatigue, and nausea - all the symptoms we describe when we talk about getting influenza.

"Cytokines also cause inflammation around the brain, causing clouded thinking, poor concentration, and can even cause feelings of depression."

McKay also listed other factors that contribute to a low mood when you're unwell.

"Headaches, muscle pain, fatigue, and nausea not only affect our mood by making us feel physically ill, but also makes us feel frustrated when we can’t do the things we want to do.

"People often manage their depression and anxiety by exercising regularly, but they can easily get an exacerbation of their symptoms when they’re stuck in bed with influenza and unable to maintain their healthy habits."

He also made a clear distinction between common cold viruses and influenza - a distinction sometimes his patients aren't so good at making themselves.

"People who have a common cold can be overzealous in their description, saying they 'have the flu' while they’re still looking chipper and turning up for work. But most people infected with influenza won’t be able to leave the house," he said.

"Common cold viruses might give you a runny nose or a sore throat, but you’ll still be able to get out of bed to make yourself a cup of tea.

"Common cold viruses cause inflammation in your nasal passage, sinuses, and respiratory tract, but the Influenza virus causes inflammation throughout your entire body.

"Influenza patients often drag themselves out of bed to see a doctor because they feel like they’re dying, often in tears because they feel so awful."

Interestingly, some researchers have a far more sinister theory when it comes to the relationship between infections like the flu and sadness. A number of studies have tried to examine whether inflammation in the body can actually trigger depression. While we don't have a clear answer yet, it's an exciting premise given that despite high rates of depression, experts are yet to fully understand the mechanisms that cause it.

Listen: Is our constant quest for happiness making us sad? Post continues after audio. 

So if you feel like the flu has taken a toll on your mental health, you're not alone, and there's a physiological reason for it. Luckily, it's likely your low mood will be transient and will shift once your body has finished fighting the infection.

But if you're worried, or your mood changes stay for longer than you'd expect, it's important to seek help from your GP.

If this story brings up issues for you, you can contact Lifeline 13 11 14 for support or beyondblue on 1300 22 4636. 

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