This Dec. 18 marks the four-year anniversary of the day Brandy Sevier donated one of her kidneys to her father for a life-saving transplant.

She was in the middle of a grueling degree program in mechanical engineering at the University of Memphis — yet she used her holiday break to undergo major surgery across the hall from her father. Her recovery took a major toll on her body, as the doctors had to pump her stomach full of air.

“A simple gift can mean the world to somebody.”

“I looked like I was pregnant when I woke up,” Sevier said. She still can’t perform crunches at the gym, and she’s had to change her diet drastically to accommodate only one kidney.

But given the chance, she would make the same choice.

“I’m the baby out of five,” she told LifeZette. “So at the time, my father hadn’t seen me graduate from college. I don’t have any kids, I haven’t been married, and I wanted him to walk me down the aisle.” Her other siblings either didn’t have kidneys that were a good match for her father, or they were struggling with their own health problems and couldn’t afford to donate one.

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Sevier spent her college semester prior to the surgery going to class, going to work, and going to the hospital, where her father was in and out of the intensive care unit (ICU). Finally, she said she told him, “I’m done watching you die in front of me.”

He felt hesitant to accept her kidney because he didn’t want her to suffer — but his situation became increasingly dire.

Sevier went through a year of tests to prepare for the donation, then finally underwent surgery shortly before Christmas 2012. “His body took my kidney like it was a piece of candy,” she said. “He was up and walking that day.”

She said his color changed almost instantly and he began to gain back the 80 pounds he had dropped during his illness. “He just turned 71 last Thursday, and he thinks he’s 35.”

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Sevier changed her major to biomedical engineering as a result of her experience, so that she could work in a field where she knew she would be helping people and potentially saving lives.

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This young woman’s story speaks to the remarkable opportunity that strangers, friends, and family members have to help others through organ or body tissue donation. On the opposite end of the country, Heather Clark from California was grieving over the death of her seven-month-old son, Lukas. She knew, however, that allowing his organs to be donated would give the gift of life to other children.

Her child’s heart went to an 18-month-old girl, Jordan Drake, who was fighting for her life in Phoenix, Arizona. Drake had suffered from seizures, a stroke, and a brain bleed because of a faulty heart valve. Now she’s four years old and full of energy. Heather Clark met with the little girl and her mother in Phoenix last January. She became emotional as she listened to her son’s heartbeat for the first time in years.

Lukas Clark also saved the lives of two other children: His liver and kidney were donated to them. “He did more in seven months in life than I’ve done in 25 years of life,” Heather Clark told USA Today.

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But life-saving gifts don’t always require donors to make the ultimate sacrifice. Trent and Erika Jones of Los Angeles, California, watched their son, Seth, suffer for seven years after being diagnosed with a rare genetic disease called diamond blackfan anemia (DBA), a failure of the bone marrow. He needed a bone marrow transplant desperately, but they couldn’t find a match on the registry. Finally he received a transplant last year — and members of his community, family, and friends wore superhero shirts to support “Super Seth” as he underwent the arduous surgery.

Now he has been able to return to school for the first time in years, and he’s able to play with and be around other children as well, instead of worrying about catching an illness that could prove fatal for his condition. “Though in our hearts we desire to be free from DBA, we have learned patience, love, trust, perseverance, compassion, courage, and to cry,” Trent and Erika Jones told the DBA Foundation.

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Brandy Sevier encourages people during this Christmas season to take the time to help others, regardless of how big or small the gesture might be.

“A simple gift can mean the world to somebody,” she told LifeZette. “If I can help somebody, I would love to do it.”

That includes donating blood or becoming a bone marrow donor, or smaller gestures such as visiting those who are sick or bedridden. She reflects on the many lives that her father has touched since he has remained alive: “If you can help somebody, it will change so many lives.”