They're related, in exactly the way you say. But they're also opposite, in that capitalism has resulted in a huge gap between rich and poor, which means the average person doesn't have the money to consume much anymore.
Our government fudges the figures by (for example) averaging what everyone makes, even though the top 10% of wage earners are pulling in 90% of the income, with not much left for the rest of us 90%. This gives a false impression of the health of the American economy. That's capitalism.
With consumerism, people are urged via heavy advertising to buy more than what they make. Government and financial regulations encourage the same, especially with easy mortgages and credit cards, both of which help people overspend. And manufacturers overuse earth's resources making more and more "stuff" for the average consumer to buy, who doesn't have the money to pay for it. The two together have produced a very strange, very self destructive system, in my view.