The Health Savings Account (HSA) is unique in the landscape of tax-preferenced investment acounts, as it is the only type that enjoys both the benefit of tax-deductible contributions and tax-free distributions (for medical expenses). In fact, the unique treatment of the HSA has created a wrinkle in the traditional approach of funding retirement accounts: given the inevitability of medical expenses in retirement, arguably the best savings account for retirement (or at least for a portion of retirement expenses) is to use a health savings account for retirement over “just” an IRA alone.
In other words, for any retiree that is saving for both medical expenses in retirement and also all of their other retirement goals, using a combination of an IRA (for most retirement expenses) supplemented by an HSA as a "retirement health savings account" may be the most tax-preferenced way to save holistically for retirement. In fact, the health savings account tax treatment is so good that it can even be superior to funding a 401(k) plan with a small match (for those who haven't already started a health savings account for retirement)!
Notably, this doesn’t mean that retirees would exclusively fund a health savings account for retirement, as the accounts are both taxable and potentially subject to penalties if used for non-medical purposes. But for those who already have some retirement accounts, and/or have more than enough dollars overall to achieve their goals, the fact remains that contributing the maximum to an HSA every year has the potential for more beneficial tax treatment than any other type of tax-preferenced account! Which makes accumulating in an HSA so desirable that it may even be preferable to pay current medical expenses out of pocket, just to preserve (and keep contributing to) the HSA account balance to be used as a future health retirement account!