The Collaborative International Dictionary of English v.0.48:

Healthiness \Health"i*ness\, n.
   The state of being healthy or healthful; freedom from
   disease.
   [1913 Webster]

WordNet (r) 3.0 (2006):

healthiness
    n 1: the state of being vigorous and free from bodily or mental
         disease [syn: good health, healthiness] [ant: health
         problem, ill health, unhealthiness]

Moby Thesaurus II by Grady Ward, 1.0:

63 Moby Thesaurus words for "healthiness":
   advantageousness, agreeableness, auspiciousness, beneficialness,
   benevolence, benignity, class, cogency, desert, eupepsia,
   excellence, expedience, fairness, favorableness, fine fettle,
   fine shape, fine whack, fineness, first-rateness, glowing health,
   good condition, good constitution, good digestion, good health,
   good shape, good trim, goodliness, goodness, grace, haleness,
   healthfulness, healthy body, healthy constitution, helpfulness,
   high feather, kindness, merit, mint condition, niceness,
   picture of health, pleasantness, profitableness, quality,
   rewardingness, robust health, rude health, rugged health,
   salubriousness, salubrity, salutariness, skillfulness, soundness,
   superiority, top shape, usefulness, validity, value, virtue,
   virtuousness, whole, wholeness, wholesomeness, worth