(Humans fed small beta-carotene supplements do not experience reduced mortality rates. This is line with animal studies which have also found no benefit for such small supplements.
The case is different with very large supplements in experimental animals A human consuming about 2000 calories/day of the hamster chow used below would be ingesting about 5 grams of beta-carotene/day. The 98% survival at 69 weeks is a record for male Syrian golden hamsters.)
Carcinogenesis 15(1): 133-136 1994
Abstract:
The study described in this paper was primarily conducted to identify the cell
types involved in the formation, progression and regression of metaplastic
changes in the repiratory tract epithelium of hamsters after intratracheal
intubations with benzo[a]pyrene. Furthermore, the role of vitamin A and
beta-carotene in these processes was studied. In the course of the study
a remarkable effect of dietary beta-carotene on survival of hamsters became
a subject of investigation. Hamsters were fed diets with various levels of
vitamin
A or beta-carotene and were treated intratracheally with a suspension of
benzo[a]pyrene with ferric oxide in saline. The tumour response of the
respiratory tract was very low (2.8%) and hyper- and metaplasia of respiratory
epithelium were virtually absent. However, an interesting observation was an
exceptionally low mortality of only 2% after 69 weeks in the group of hamsters
fed a high beta-carotene diet (1% w/w), whereas in the other groups mortality
after 69 weeks amounted to 25%. Although the exact cause of death of most
of the hamsters could not be established, a 40% reduction of lipid peroxidation
in the livers was found in the high beta-carotene group. Moreover, in this group
the degree and incidence of nephrosis and of focal mineralization of kidneys
and heart were lower than in the other groups. These favourable effects of
the high beta-carotene diet may have contributed to the unusually high
survival rate in hamsters fed this diet. Further studies are planned to verify
and study this observation.