Vitamin D is technically labeled a vitamin, but it behaves more like a hormone. It influences hundreds of genes and plays a role in immune function, mood regulation, bone strength, and inflammation balance.
Unlike most nutrients, vitamin D is primarily produced through sun exposure. However, indoor lifestyles, sunscreen use, geographic location, and seasonal changes all limit production. As a result, deficiency is widespread.
Low vitamin D levels may show up as fatigue, low mood, frequent illness, slow recovery, or weakened bones. Because vitamin D receptors exist throughout the body, its impact extends far beyond skeletal health.
What makes vitamin D unique is its ability to help regulate immune response. It does not simply stimulate immunity. It helps balance it. That means supporting appropriate defense without excessive inflammatory response.
Fatty fish, egg yolks, and fortified foods provide small amounts, but for many people, supplementation is necessary to maintain healthy levels year round.