The findings questioned previous Norwegian research that suggested childhood cod liver oil consumption might have an adverse effect on bone mineral density (BMD) in elderly women, which could be due to high retinol vitamin A content of the oil.
However the researchers from the Icelandic Heart Association, the University of Iceland and Landspitali National University Hospital as well as the National Institute of Ageing in the US said studies on this were few and results unclear.
This latest Reykjavik study looked at 4798 participants aged 66-96 years and their reported retrospective cod liver oil intake during adolescence and midlife as well as current intakes in older age using a food frequency questionnaire. Hip bone mineral density (BMD) and vitamin D blood levels were then recorded.
Writing in the British Journal of Nutrition, the researchers said: "We found no evidence that cod liver oil intake at any age might be harmful to hip BMD in old age."
A slight different was seen for women compared to counterparts consuming less of the oil. Yet the researchers said the difference was so small its clinical relevance was questionable.
Meanwhile oil intakes in older age was positively associated with vitamin D serum levels. Those with intakes of less than once per week, one - six times per week and every day had vitamin D concentrations of about 40, 50 and 60 nanomole per litre (nmol/l), respectively.
Old age daily intake of cod liver oil intake was associated with an increase of about 20 nmol/l in vitamin D levels compared to no intake or less than once a week.
Iceland is located 62-67 degrees North, meaning little to no vitamin D can be synthesised in the skin from around October to April.
They said cod liver oil was a traditional source of vitamin D in Iceland and was regularly recommended for bone health meaning it was in the interest of public health to explore the true impact of lifelong consumption on bone health.
"The significance of cod liver oil intake at various ages for the ultimate old age bone health warrants further studies, especially on intakes during childhood and adolescence, as cod liver oil is supplied in several schools and child care centres in Iceland for public health purposes."
The researchers questioned whether a "more profound relationship" between old age intake and hip BMD might have been masked by the relatively high average vitamin D levels of the participants even among those who did not take cod liver oil or other vitamin D supplements.
The paper was part of the Age, Gene/Environment Susceptibility (AGES) Reykjavik Study.
Source: British Journal of Nutrition
Published online ahead of print, DOI: http://dx.doi.org/10.1017/S0007114515001397
"Cod liver oil consumption at different periods of life and bone mineral density in old age"
Authors: T. Eysteinsdottir, T. I. Halldorsson, I. Thorsdottir, G. Sigurdsson, S. Sigurdsson, T. Harris, L. J. Launer, V. Gudnason, I. Gunnarsdottir and L. Steingrimsdottir