On 2015 Mar 30, John Cannell commented:

In Denmark, like all Scandinavian countries, the use of cod liver oil is common. Cod liver oil will raise 25(OH)D levels but also increase vitamin A intake. Increased vitamin A intake has been associated with increased mortality. This would explain the J shaped relationship found by the authors.

Bjelakovic G, Nikolova D, Gluud LL, Simonetti RG, Gluud C. supplements for prevention of mortality in healthy participants and patients with various diseases. Cochrane Database Syst Rev. 2008 Apr 16;(2):CD007176.

On 2015 Mar 30, John Cannell commented:

In Denmark, like all Scandinavian countries, the use of cod liver oil is common. Cod liver oil will raise 25(OH)D levels but also increase vitamin A intake. Increased vitamin A intake has been associated with increased mortality. This would explain the J shaped relationship found by the authors.

Bjelakovic G, Nikolova D, Gluud LL, Simonetti RG, Gluud C. supplements for prevention of mortality in healthy participants and patients with various diseases. Cochrane Database Syst Rev. 2008 Apr 16;(2):CD007176.