B9

B9 is a designation used in several different contexts across nutrition, music, and popular culture.

In nutrition, Vitamin B9 refers to folate, and in its synthetic form folic acid. It is a water-soluble B vitamin essential for one-carbon metabolism, DNA synthesis and repair, and red blood cell formation. Folate occurs naturally in leafy greens, legumes, and some fruits, while many countries fortify foods with folic acid to reduce deficiency risk. Adequate intake is particularly important during pregnancy to help prevent neural tube defects in the developing fetus. Deficiency can lead to megaloblastic anemia and other health issues, and recommended daily allowances vary by age, sex, and life stage.

In music theory, B9 denotes a dominant ninth chord built on the note B. This chord typically includes the notes B, D-sharp, F-sharp, A, and C-sharp, though voicings can vary. The major third and major ninth above the root, along with a minor seventh, give the chord a tense, colorful sound commonly used in jazz, funk, and fusion styles.

In popular culture, B-9 is the designation of the robot character in the 1960s science fiction television series Lost in Space. The B-9 robot is known for its cylindrical design and the catchphrase, “Danger, Will Robinson,” and serves as a memorable element of the show’s ensemble cast.