Robert De Niro has given the authors of a book about his artist father access to intimate journals written by the painter, even though he can’t face reading them himself.

The journals reveal what the Oscar-winning actor describes as his father’s “demons”, including De Niro Sr’s struggle to make enough money and to find artistic recognition, as well as his anxieties over his mental health and his homosexuality, which broke up his marriage to a fellow artist when their son was a toddler.

Robert De Niro Sr died in 1993, leaving behind four notebooks filled with his inner thoughts, written over 10 years from 1963. A prominent figure in the New York art world of the 1940s and 50s, he painted landscapes, still-lifes and portraits, using a mix of abstract and expressionist styles in the boldest colours. He found inspiration in Matisse, among other artists.

Talking about the journals, his son told the Observer: “I’m anxious to read them. I’ll read them when it feels right … but at the moment that’s how I’m dealing with it.”

He has instead made them available to art historians working on a book, titled Robert De Niro, Sr: Paintings, Drawings and Writings: 1942-1993, which will be published by Rizzoli next month.

Portrait of Mrs. Z, 1959, and Last Painting, 1985-93, by Robert De Niro Sr. Photograph: © The Estate of Robert De Niro, Sr. / Artists Rights Society (ARS), New York.

Having read only excerpts which had been singled out for the publication, De Niro said: “It was sad for me to read. He had his demons … I was sorry.”

In one passage, his father wrote of praying “until I am cured of my mental and emotional sickness”, adding: “If God doesn’t want me to be homosexual (about which I have so much guilt), he will find a woman whom I will love and who will love me. But I really don’t want my homosexuality to be cured.”

Elsewhere he said: “I am full of fear ... of the discomfort caused by my own thoughts, feelings, sensations and impulses.” He even questioned the validity of keeping a journal: “There is so much I have left out of this journal … My laments, wailings, self-pity and complaining are much greater than I have [indicated] here.”

Such passages are all the more difficult for his son to read as De Niro Sr did not discuss his anxieties with him, or at least only in “vague ways”.

Although his father’s works were acquired by the Metropolitan Museum of Art and the Whitney Museum of American Art, among other galleries, De Niro Sr lived “a classic artist’s life in a studio that was a mess”, his son recalls.

Robert De Niro Sr at work in his studio in New York, circa 1980. Photograph: Sonia Moskowitz/Images Press/Getty Images

Born in Syracuse, New York, into an Irish-Italian household, De Niro Sr was a child prodigy. In 1933, aged 11, he started taking classes at the Syracuse Museum of Fine Arts, which even gave him his own room in which to work. Later, his admirers included the art patron Peggy Guggenheim. His debut solo exhibition, when he was 23, inspired leading critic Clement Greenberg to write: “Guggenheim has discovered another important young abstract painter.”

In the book, former museum curator Charles Stuckey describes De Niro Sr as among the most respected artists in the New York of the 1940s and 1950s: “But like many of his equally ambitious contemporaries … De Niro has too often been omitted from accounts of the so-called New York School.” The book notes that the artist experienced financial and professional hardships throughout his life.

His son has been described as the greatest movie actor of his generation. His latest film, The Irishman, marks his ninth feature film with Martin Scorsese. The pair worked on Taxi Driver, for which De Niro was nominated for an Oscar, and Raging Bull, for which he won the award.

De Niro said of his father: “When I started doing well in acting, I helped him.” Asked whether his father’s struggle was all the more difficult against his own success, he said: “He was very proud of me. At the same time, part of him might have been saying, ‘I wish I had some success too’. He always used to say to me ‘great artists are recognised many, many years after they’re gone’.”

Still Life, circa 1946, and Anna Christie Entering the Bar, 1976, by Robert De Niro Sr. Photograph: © The Estate of Robert De Niro, Sr. / Artists Rights Society (ARS), New York.

Growing up, De Niro did not realise his father’s torment over his homosexuality: “I wasn’t aware of that … My mother told me once later, when I was a young adult, sort of inferred. I sort of understood.”

Father and son shared a pride in each other’s work, never feeling the need to express it in words: “It wasn’t like we sat down and he told me, ‘I like this movie’ … But I know he was proud.”

Robert De Niro Sr. Paintings, Drawings and Writings: 1942-1993, will be published in October.

In the journals, De Niro Sr refers to his son, writing that he was “getting all sorts of movie and stage offers”, and adding: “My little baby-doll has grown up.”

In another passage, he wrote of his son: “He is tanned from a sunlamp – for his new movie part – and looks much better than when he returned from Italy two weeks ago. I wanted to run my fingers through his hair and to kiss him, but I hardly think that he would have appreciated it.”

In 2014, De Niro made an HBO documentary on his father. The journals were cited, but only a tiny percentage has been published.