3 top long-term ISA holdings: GlaxoSmithKline plc, Unilever plc and City of London Investment Trust plc

Today I'm looking at three 'core' ideas for investors who are looking for long-term growth within their ISAs.

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Dividend champion

With Europe facing an ageing population, I believe healthcare stocks could offer an attractive long-term investment theme.

GlaxoSmithKline's (LSE: GSK) appeal lies in its potential for long-term growth as global pharmaceutical sales rise, combined with a formidable 5.4% dividend yield.

While patent expiries in the last few years have seen revenues plateau, the pharmaceuticals giant has a product pipeline of over 40 new medicines and vaccines that have the potential to drive revenues going forward.

A favourite of prominent fund manager Neil Woodford, GlaxoSmithKline has rewarded shareholders with annualised returns of around 8.3% over the last five years and the company is well placed to deliver further gains in the future.

Everyday essentials

For a long-term holding, it's hard to look past multinational consumer goods giant Unilever (LSE: ULVR).

Unilever owns a portfolio of over 400 brands, including Dove, Flora and Ben & Jerry's and I can't see demand for these types of 'everyday' products declining any time soon. While technology may be rapidly changing the world, people are still going to buy products such as soap and ice cream for the foreseeable future.

Unilever has performed admirably over the long term, with shareholders enjoying total annualised returns of almost 14% per year over the last five years. For this reason, the company is popular with both fund managers and private investors, and the high demand for its shares means that the stock generally trades at a premium to the market average.

Indeed, Unilever's current P/E ratio is a high 23.8, a level that Neil Woodford has described as "ludicrous".

Successful investing is all about buying assets at the right price, and for that reason, I would be waiting for a pull-back before buying shares in Unilever.

The perfect core holding?

For a rock-solid core portfolio holding, I believe it's hard to look past the City of London Investment Trust (LSE: CTY).

Unlike GlaxoSmithKline and Unilever, this isn't an individual stock, but an investment trust containing a portfolio of around 115 stocks. The trust's objective is to provide long-term growth in income and capital, and places a strong focus on dividend income for its investors.

City of London Investment Trust has been run by Henderson Global Investors' Job Curtis since 1991, a fund manager who takes a value-oriented, conservative approach to investing. Curtis scours the market for well capitalised companies with dividend growth potential, and this approach has enabled the trust to outperform its benchmark on a consistent basis, and provide investors with an excellent dividend yield. The trust's yield currently sits at around 4.15% and the dividend payout has been increased every year since 1966.

While the trust predominantly invests in blue-chip companies such as British American Tobacco, Royal Dutch Shell, HSBC and Vodafone, it is allowed to invest in smaller FTSE 350 companies and therefore has access to companies with higher growth potential.

With a low fee of just 0.42% per year, in my mind it's hard to beat the City of London Investment Trust as a core portfolio holding, as the trust provides the perfect mix of 'sleep well at night' security with an excellent dividend payout.

Of course, these are just three ideas that could help in building a strong long-term portfolio.

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Edward Sheldon owns shares in GlaxoSmithKline. The Motley Fool UK owns shares of and has recommended GlaxoSmithKline and Unilever. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors.