The fifth series of the hit show returned earlier this month and sees character Doctor Dwight Enys take an interest in mental health following the death of his daughter, Sarah.
Horsfield, who adapted the series from Winston Graham’s Poldark novels, told Radio Times magazine that mental health issues can strike anyone, at any time and a taboo about them still exists.
"After the birth of my first child, it didn't occur to me to talk about the permanent 'fog' I felt I was wading through, let alone consider it a form of post-natal depression,” she said.
"When I eventually confided in a family member, she actually got up and ran out of the room!
"This was something of a blow... until I realised that the person concerned had probably struggled with that same issue herself...
The writer said that the experience gave her “insight into the challenges involved in acknowledging and addressing the stigma and fear surrounding the subject”.
The NHS states that postnatal depression is a type of depression that many parents experience after having a baby.
The condition is expected to affect more than one in every 10 women within a year of giving birth and can affect also affect partners and fathers. Symptoms of postnatal depression can include a persistent feeling of sadness and low mood, problems concentrating and making decisions, and difficulty sleeping.
Since Sunday night's episode, several Twitter users have praised the show for exploring mental health issues.
“Loving the fact they are dealing with #mentalhealth with the insanity side plot,” one user wrote.
Another added: “Dr. Dwight looking out for mental health. A man ahead of his time.”
— Marlena Kellie (@marlenakellie)July 21, 2019
Dr. Dwight looking out for mental health. A man ahead of his time #Poldark— Becca. (@RebeccaWard22)July 21, 2019
Earlier this month, actor Luke Norris, who plays Dr Enys in the show, opened up about his character’s interest in mental health in this series following the medical expert’s struggle with post-traumatic stress disorder and bereavement.
"He goes into the royal college of surgeons as someone who is interested in mental health,” Norris said during the premiere of the fifth series. “And obviously at the time, and even now, it is quite a taboo subject. It is a difficult subject.”
Horsfield continued, stating that she hoped the new and final BBC One series will encourage viewers to open up about any mental health issues they have.
The full interview is in this week's Radio Times magazine.
If you have been affected by any issues mentioned in this article, you can contact the following mental health organisations: