Adjusted results exclude special items that affect comparisons with reported results.
Finally, all references in today's remarks to tobacco consumers or consumers within a specific tobacco category or segment, refer to existing adult tobacco consumers 21 years of age or older.
oral nicotine pouches as we recently closed transactions to acquire the remaining 20% global interest.
Tom served 13 distinguished years on our board, offered valuable insights and guidance during his tenure, and was a true visionary.
Our first-quarter adjusted diluted earnings per share declined 1.8%, primarily driven by unfavorable timing of interest expense and a higher adjusted income tax rate.
For volumes, reported smokeable segment domestic cigarette volume declined 12% in the first quarter, reflecting year-over-year trade inventory movements, one fewer shipping day and other factors.
When adjusted for these factors, cigarette volume declined by an estimated 3.5%.
We believe that in the first quarter of 2020, wholesalers built inventories by approximately 900 million units, driven in part by COVID-19 dynamics, compared with a depletion of approximately 300 million units in the first quarter of 2021.
At the industry level, we estimate that first-quarter adjusted domestic cigarette volume declined 2%.
We completed transactions in December and April to acquire the remaining 20% of the global on!
business for approximately $250 million.
When we made the initial 80% acquisition in 2019, the oral nicotine pouch category in the U.S. was rapidly growing off of a small base.
In the first quarter of 2021, we estimate that retail share for all nicotine pouches was approximately 13% of the total oral tobacco category, double its share in the year ago period.
We expect continued growth from the oral nicotine pouch products and estimate that category volume in the U.S. will grow at a compounded annual growth rate of approximately 25% over the next five years.
Helix achieved an annualized manufacturing capacity of 50 million cans by the end of last year, and as of the end of the first quarter, on!
was sold in approximately 93,000 stores.
share of the total oral tobacco category grew significantly to 1.7%.
retail share was 3.1%, an increase of seven-tenth from the 2020 full-year share.
share of the total U.S. oral tobacco category as Helix expects to be in stores covering 90% of the industry's oral tobacco volume by midyear.
We estimate that total category volume increased 24% versus the year ago period.
Sequentially, we estimate that the category volume increased 7% as competitive marketplace activity continued.
As a result of these dynamics, JUUL's first-quarter retail share of the total e-vapor category decreased to 33%.
In Atlanta stores with distribution, Marlboro HeatSticks retail share of the cigarette category was 1.1%, an increase of two-tenth sequentially and in Charlotte, HeatSticks retail share was 1%, an increase of three-tenth sequentially.
Last month, PM USA began selling the IQOS 3 device, which offers a longer battery life and faster recharging, as compared to the 2.4 version.
We're encouraged to see that many consumers are upgrading their 2.4 devices, representing approximately 25% of all IQOS 3 device sales in the first quarter.
Along with geographic expansion, PM USA is increasing the use of its digital platforms like Marlboro.com and getiqos.com to engage with smokers and communicate the benefits of IQOS, including the MRTP claim on the IQOS 2.4 system.
We reaffirm our 2021 guidance to deliver adjusted diluted earnings per share in a range of $4.49 to $4.62.
This range represents an adjusted diluted earnings per share growth rate of 3% to 6% from a $4.36 base in 2020.
The smokeable products segment delivered over $2.3 billion in adjusted OCI and expanded adjusted OCI margins by 2.2 percentage points to 57.5%.
PM USA's revenue growth management framework supported the segment's strong net price realization of 8% for the quarter.
In the first quarter, Marlboro's retail share was 43.1%, an increase of four-tenth versus prior year.
In the first quarter, Marlboro's price gap to the lowest effective price cigarette increased to 37%, primarily driven by heavy competitive promotional activity in the branded discount segment.
The total discount segment retail share was 25.3%, an increase of one-tenth versus the year ago period.
Middleton's reported cigar shipment volume increased over 11% in the first quarter.
Oral tobacco products segment, adjusted OCI grew by 3.1%, and adjusted OCI margins declined by 0.9 percentage points to 72.1%.
Total reported Oral Tobacco Products segment volume increased 0.6%, driven by on!
When adjusted for trade inventory movements, calendar differences and other factors, segment volume increased by an estimated 0.5%.
First-quarter retail share for the oral tobacco products segment was 48.1%, down 2.3 percentage points due to the continued growth of oral nicotine pouches.
Michelle's first-quarter adjusted OCI increased approximately 46% to $19 million, driven primarily by higher pricing and lower costs.
And in beer, we recorded $190 million of adjusted equity earnings in the first quarter, which was unchanged from the year-ago period and represents Altria's share of API fourth-quarter 2020 results.
We recorded an adjusted loss of $27 million representing Altria's share of Cronos' fourth-quarter 2020 results.
And finally, on capital allocation, we paid approximately $1.6 billion in dividends and repurchased approximately 6.9 million shares, totaling $325 million in the first quarter.
We have approximately $1.7 billion remaining under the currently authorized $2 billion share buyback program, which we expect to complete by June 30, 2022.
Our balance sheet remains strong and as of the end of the first quarter, our debt-to-EBITDA ratio was 2.5 times.
We issued new long-term notes totaling $5.5 billion and repurchased over $5 billion in outstanding long-term notes.
In May, we expect to retire $1.5 billion of notes coming due with available cash.

Summary:
Adjusted results exclude special items that affect comparisons with reported results.
oral nicotine pouches as we recently closed transactions to acquire the remaining 20% global interest.
We completed transactions in December and April to acquire the remaining 20% of the global on!
We reaffirm our 2021 guidance to deliver adjusted diluted earnings per share in a range of $4.49 to $4.62.
This range represents an adjusted diluted earnings per share growth rate of 3% to 6% from a $4.36 base in 2020.
In May, we expect to retire $1.5 billion of notes coming due with available cash.